Methods to increase or decrease bone density

ABSTRACT

The SOST gene gives rise to sclerostin, a protein that leads to apoptosis of bone progenitor cells. The invention provides antagonists to the sclerostin protein, and methods for identifying new sclerostin antagonists. The invention also provides molecules that can depress expression of the SOST gene, as well as methods for identifying such molecules. Such molecules and antagonists are useful for increasing bone mineralization in mammals, for example, in the treatment of osteoporosis.

This application claims priority from U.S. application Ser. No. 60/361,258 filed Mar. 1, 2002, from U.S. application Ser. No. 60/406,171 filed Aug. 27, 2002 and from U.S. application Ser. No. 60/447,393 filed Feb. 13, 2003.

FIELD OF THE INVENTION

The invention provides compositions and methods for modulating bone density. Methods for identifying new compounds that can modulate bone density are also provided.

BACKGROUND OF THE INVENTION

Osteoporosis is a bone disorder characterized by the loss of bone mass, which leads to fragility and porosity of the bone of man. As a result, patients suffering from osteoporosis have an increased fracture risk of the bones. Postmenopausal women are particularly at risk for osteoporosis as a result of reduced levels of estrogen production. When administered at low levels, estrogens have a beneficial effect on the loss of bone. However, estrogen replacement therapy can have unwanted side effects including an increased risk of blood clots, breast carcinomas, endometrium hyperplasia, and an increased risk of endometrium carcinomas. Ate remaining current therapies provide little in terms of generating new bone for osteoporotic patients. Hence, a need exists for an alternative treatment of osteoporosis.

Sclerosteosis is a genetic disease resulting in increased bone formation and the development of strong skeletons in humans. Sclerosteosis is caused by a loss of function or null mutation in the SOST gene (Beighton et al. 1976; Brunkow et al. 2001; Balesman et al. 2001). The majority of affected individuals have been reported in the Afrikaner population of South Africa, where a high incidence of the disorder occurs as a result of a founder effect. Homozygosity mapping in Afrikaner families along with analysis of historical recombinants localized sclerosteosis to an interval of approximately 2 cM between the loci D17S1787 and D17S930 on chromosome 17q12-q21. Affected Afrikaners carry a nonsense mutation near the amino terminus of the encoded protein, whereas an unrelated affected person of Senegalese origin carries two splicing mutations within the single intron of the gene.

The SOST gone encodes a protein called sclerostin that shares some sequence similarity with a class of cystine knot-containing factors including dan, cerberus, gremlin, prdc, and caronte. The sclerostin protein gene is thought to interact with one or more of the bone morphogenetic proteins (BMPs) (Brunkow et al, 2001). Bone morphogenetic proteins are members of the transforming growth factor (TGF-β) superfamily that have been shown to play a role in influencing cell proliferation, differentiation and apoptosis of many tissue types including bone. Bone morphogenetic proteins can induce de novo cartilage and bone formation, and appear to be essential for skeletal development during mammalian embryogenesis (Wang 1993). Early in the process of fracture healing the concentration of bone morphogenetic protein-4 (BMP-4) increases dramatically (Nakase et al. 1994 and Bostrom et al. 1995). In vivo experiments indicate that up-regulation of BMP-4 transcription may promote bone healing in mammals (Fang et al. 1996). Bone morphogenetic proteins have been reported to induce the differentiation of cells of the mesenchymal lineage to osteogenic cells as well as to enhance the expression of osteoblastic phenotypic markers in committed cells (Gazzero et al. 1998, Nifuji & Noda, 1999). The activities of bone morphogenetic proteins in osteoblastic cells appear to be modulated by proteins such as noggin and gremlin that function as bone morphogenetic protein antagonists by binding and inactivating bone morphogenetic proteins (Yamaguchi et al. 2000).

However, the cascade of events leading to bone mineralization and the factors that control bone density are not completely understood. A need exists for factors that can modulate the differentiation of osteoblastic cells, promote bone mineralization and improve bone density.

SUMMARY OF THE INVENTION

According to the invention, the sclerostin protein encoded by the SOST gene is a unique bone morphogenetic protein antagonist and an important regulator of bone matrix formation. The SOST gene is expressed at high levels by committed, mature osteoblasts but at low or non-existent levels in immature and undifferentiated osteoblasts. Also according to the invention, the sclerostin protein blocks the ability of osteoprogenitor cells to differentiate, to deposit mineral and to express proteins characteristic of fully mature osteoblasts, for example, collagen and alkaline phosphatase. The expression of SOST is modulated by steroids and is regulated by bone morphogenetic proteins, for example, bone morphogenetic factors 2, 4 and 6. While bone morphogenetic factors increase the activity of osteoblastic markers such as alkaline phosphatase, the SOST gene product (sclerostin) blocks the activity of such osteoblastic markers. Moreover, bone morphogenetic factors can reverse the sclerostin-induced decrease in osteoblastic activity.

The invention provides pharmaceutical compositions for decreasing SOST expression in a mammal comprising a therapeutically effective amount of a compound of the formula I:

wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ are separately carbonyl, halo, fluorine hydrogen, hydroxyl, lower acyl, lower alkoxy, lower alkyl, or lower hydroxy alkyl. In some embodiments, the R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ groups can separately be carbonyl, hydroxy, hydrogen, or lower hydroxy alkyl. In other embodiments, R₁ is carbonyl or hydroxy and/or R₈ is fluorine, hydrogen or halo.

The invention further provides a pharmaceutical composition for decreasing SOST expression in a mammal comprising a therapeutically effective amount of a glucocorticoid. The glucocorticoid can be, for example, fluocinolone acetonide, triamcinolone or dexamethasone.

The invention also provides a pharmaceutical composition for decreasing SOST expression in a mammal comprising a therapeutically effective amount of a prostaglandin comprising formula II:

wherein R₁₀, and R₁₁ are separately carbonyl, halo, fluorine, hydrogen, hydroxyl, lower acyl, lower alkoxy, lower alkyl, lower hydroxy alkyl, aryl or aryloxy. R₁₀ and R₁₁ can also separately be carbonyl, hydroxy, hydrogen, or lower hydroxy alkyl. The prostaglandin can be, for example, prostaglandin E2.

The invention also provides a pharmaceutical composition for decreasing SOST expression in a mammal comprising a therapeutically effective amount of a bile salt of formula III:

wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈ and R₉ are separately carbonyl, halo, fluorine, hydrogen, hydroxyl, lower acyl, lower alkoxy, lower alkyl, or lower hydroxy alkyl. R₁, R₂, R₃, R₄, R₅, R₆, R₇ and R₉ can also separately be carbonyl, hydroxy, hydrogen, or lower hydroxy alkyl. An example of such a bile salt is ursodeoxycholic acid.

The invention also provides a pharmaceutical composition for decreasing SOST expression in a mammal comprising a therapeutically effective amount of a prostaglandin such as prostaglandin E2, a bile salt such as ursodeoxycholic acid, or a glucocorticoid such as fluocinolone acetonide, triamcinolone or dexamethasone.

The invention further provides a method for decreasing SOST expression in a mammal that comprises administering to the mammal a therapeutically effective amount of a prostaglandin such as prostaglandin E2, a bile salt such as ursodeoxycholic acid, or a glucocorticoid such as fluocinolone acetonide, triamcinolone or dexamethasone.

The invention also provides a method for increasing bone density in a mammal that comprises administering a therapeutically effective amount of ursodeoxycholic acid, fluocinolone acetonide, triamcinolone, prostaglandin E2 or dexamethasone to the mammal. In one embodiment, the methods of the invention can be practiced with a steroid or a glucocorticoid hormone. Examples of such glucocorticoid hormones include cortisol, dexamethasone and structurally related compounds. An example of a therapeutically effective amount of a glucocorticoid hormone is a blood concentration of about 0.01 micromolar to about 1 micromolar.

The invention further provides a pharmaceutical composition for decreasing SOST expression in a mammal comprising a therapeutically effective amount of an anti-sense nucleic acid capable of hybridizing to SEQ ID NO:1, 2, 4, 5 or 7.

The invention also provides a pharmaceutical composition that comprises a therapeutically effective amount of a sclerostin antagonist. Such a sclerostin antagonist can be an antibody that can bind a sclerostin polypeptide having SEQ ID NO:3 or SEQ ID NO:6 or SEQ ID NO:8. Another example of such a sclerostin antagonist is a peptide of a bone morphogenetic protein that binds to sclerostin.

The invention further provides a method for identifying a factor that decreases SOST expression comprising: providing a cell that comprises a nucleic acid construct comprising a SOST promoter having SEQ ID NO:4 that is operably linked to a nucleic acid encoding a detectable marker; contacting the cell with a test sample containing a factor; and detecting whether a factor in the test sample decreases expression of the detectable marker relative to a control that comprises the cell that has not been contacted with a test sample. For example, such a cell line is any cell line responsive to a bone morphogenetic protein. Another example of such a cell is a C2C12 cell line having ATCC Deposit No. CRL-1772 or a C3H10T1/2 cell line having ATCC Deposit No. CCL-226 or a human mesenchymal (hMSC) cell. Another element that can be present in the nucleic acid construct is an osteoblastic-specific steroid response element.

The invention also provides a method for identifying a factor that decreases SOST expression comprising contacting a cell with a test sample and detecting whether a factor in the test sample decreases endogenous SOST expression. In this method, SOST expression can be from a nucleic acid comprising SEQ ID NO:1 or SEQ ID NO:2 or SEQ ID NO:5 or SEQ ID NO:7. In another embodiment of this method, SOST expression can be from a nucleic acid encoding a protein comprising SEQ ID NO:3 or SEQ ID NO:6 or SEQ ID NO:8.

The invention further provides a method for identifying an antagonist for sclerostin comprising contacting a cell with both sclerostin and a test sample and detecting whether the test sample prevents apoptosis of the cell.

The invention also provides a method for identifying a molecule that binds to sclerostin comprising contacting a test sample with a sclerostin polypeptide comprising SEQ ID NO:3 or SEQ ID NO:6 or SEQ ID NO:8 and determining whether a molecule in the test sample binds to the polypeptide.

DESCRIPTION OF THE FIGURES

The twenty-seven figures of the application illustrate the results of experiments that define the importance of SOST and its gene product, sclerostin, in the regulation of bone homeostasis. In general, FIGS. 1 to 9 show that SOST is expressed by mature osteoblastic cells and that its expression is modulated by important bone growth factors and steroids. FIGS. 10 to 19 demonstrate the inhibitory effect of sclerostin on the activity of osteoblastic markers. Finally, FIGS. 20 to 27 show that sclerostin affects the viability and the survival of osteoblastic bone cells.

FIG. 1A provides a Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) analysis of SOST expression compared to the expression of other factors. The RNA used as a template for RT-PCR was prepared from primary human osteoblasts, undifferentiated hMSC cells and hMSC cells differentiated to yield osteoblasts, chondrocytes and adipocytes. RT-PCR amplification products were separated and visualized on an agarose gel. The cell type from which the RNA template was obtained is shown at the bottom of the gel shown in FIG. 1A. Several sets of primers were used in separate RT-PCR reactions to compare the level of SOST expression in the various cell types with the level of expression of characteristic phenotypic markers for various cell types, including parathyroid hormone receptor (PTHr), collagen (types I, X and IX), PPARγ2 (a characteristic phenotypic marker for adipocytes) and Defender Against Death (DAD, a housekeeping gene). As can be observed in FIG. 1A, undifferentiated hMSC cells and adipocytes expressed negligible levels of SOST. In contrast, the cell types capable of mineralization that express markers associated with the osteoblast and hypertrophic chondrocyte phenotype (e.g. type I collagen and type X collagen, respectively) did express SOST.

FIG. 1B illustrates that SOST is expressed at higher levels in mature osteoblasts. Human MSC cells were grown in regular growth medium (Undifferentiated) or Osteoblast-Inducing medium (Differentiated) for 21 days. Matching cultures were stopped at 7 or 21 days and stained histochemically for alkaline phosphatase (ALP) or collagen (Masson Trichrome stain). Other cultures were processed for RT-PCR analysis of SOST expression. hMSC cells that had differentiated into osteoblasts were identified by enhanced histochemical staining for alkaline phosphatase (ALP) and collagen (FIG. 1B, purple and blue stains respectively in the original photographs of the differentiated cells in the right panel at 21 days) and deposition of mineral (negligible at Day 7 versus 437±60 μg calcium/mg protein at Day 28). Undifferentiated hMSC cells expressed negligible levels of SOST mRNA as well as negligible levels of alkaline phosphatase activity, and low collagen and, mineral deposition (FIG. 1B, left two panels). In contrast, the expression of alkaline phosphatase, collagen and SOST increased with time in cells grown in osteoblast-inducing media.

FIG. 2 illustrates that SOST expression is up-regulated by bone morphogenetic proteins (BMPs). RNA was isolated for RT-PCR analysis of SOST expression from hMSC cells treated with various factors, including insulin-like growth factor-1 (IGF-1, 10 or 50 ng/ml), 1,25-dihydroxyvitamin D₃ (vit D, 10⁻⁷M), dexamethasone (DEX, 10⁻⁷M), BMP-6 (300 ng/ml), or BMP-4 (50 or 300 ng/ml), for 72 hrs. RNA was also isolated for RT-PCR analysis of SOST expression from cells grown for 7 or 21 days in regular growth media (Control) or Osteoblast-Inducing media (induced). As illustrated, while untreated hMSC cells (“vehicle”) strongly expressed type I collagen, such cells had negligible levels of PTHr and SOST (Vehicle and Control, 21 days). These results indicate that untreated hMSC cells are in an early stage of osteoblast lineage, but are committed to osteoblastogenesis. Treatment of these cells with DEX, BMPs, IGF-1 (IGF-1 at 50 ng/ml) or long-term culture in osteoblast-inducing media (Induced, 21 days) advanced the stage of differentiation and induced PTHr expression. Several factors enhanced the expression of SOST, including BMP-4, BMP-6, and IGF-1 (50 ng/ml). FIG. 3 illustrates that bone morphogenetic proteins up-regulate SOST expression and also provides a time course of such BMP-induced SOST expression in hMSC and primary human osteoblasts. Cells were treated with BMP-2 (100 ng/ml) or BMP-4 (50 ng/ml) for 24 to 120 hrs prior to harvesting for RNA and RT-PCR analyses. As shown, maximum levels of SOST expression were achieved within 72 to 120 hrs after the start of treatment.

FIG. 4 illustrates the effects of bone morphogenetic proteins 2, 4 and 6 on the expression of BMP antagonists gremlin, noggin, and SOST in hMSC cells. hMSC cells were treated with BMPs 2, 4 and 6 (100 ng/ml) for 72 hrs prior to harvesting RNA and performing RT-PCR analyses. Two cDNA controls were run for the noggin analysis. While the basal levels of SOST and noggin were negligible in undifferentiated hMSC cells, the expression of SOST and noggin was up-regulated by BMPs-2, 4 and 6. In contrast, gremlin was constitutively expressed in undifferentiated hMSC cells and its expression was only modestly increased by the bone morphogenetic proteins.

FIG. 5 illustrates that steroids can modulate the effect of bone morphogenetic protein-4 on SOST expression. RNA was isolated from hMSC cells treated for 72 hrs with 1,25-dihydroxyvitamin D₃ (vit D, 10⁻⁷M), retinoic acid (RA, 10⁻⁶M), BMP-4 (250 ng/ml), dexamethasone (DEX, 10⁻⁷M), or a combination of BMP-4 with these steroids. The isolated RNA was then analyzed for SOST by RT-PCR. BMP-4 alone enhanced SOST expression. Retinoic acid and vitamin D enhanced the levels of SOST when added in combination with BMP-4—the levels of SOST were greater when retinoic acid or vitamin D was present with BMP-4 than when in cells were treated with BMP-4 alone. Dexamethasone abolished the stimulatory effect of BMP-4 on SOST expression.

FIG. 6 provides a comparison of the effects of steroids on the expression of gremlin, noggin, and SOST in hMSC cells. hMSC cells were treated for 72 firs with BMP-4 (100 ng/ml), retinoic acid (RA, 10⁻⁶M), dexamethasone (DEX, 10⁻⁷M), and 1,25-dihydroxyvitamin D₃ (vit D, 10⁻⁷M) or a combination of BMP-4 with retinoic acid, dexamethasone or vitamin D. RNA was then harvested from the cells and RT-PCR analyses were performed. BMP-4 enhanced the expression of gremlin and noggin. The steroids had small effects on BMP-induced noggin and gremlin expression. As illustrated, BMP-4 also significantly increased the levels of SOST expression. This effect on SOST expression was enhanced by the presence of vitamin D or retinoic acid but was depressed by the presence of dexamethasone.

FIG. 7 provides a photograph of a gel illustrating the effects of glucocorticoid analogs and a bile salt on the expression of SOST in hMSC cells. hMSC cells were treated with BMP-6 (250 ng/ml) in the absence or presence of dexamethasone (DEX, at 10⁻⁷M), triamcinolone (Triam, at 10⁻⁷M), ursodeoxycholic acid (Urso-1 at 1×10⁻⁶M or Urso-2 at 3×10⁻⁶M) for 72 hrs. RNA was isolated and analyzed by RT-PCR for SOST. The DAD gene was used as a control for DNA loading. Dexamethasone, triamcinolone, ursodeoxycholic acid blocked the induction of SOST by BMP-6.

FIG. 8 provides a photograph of a gel illustrating the effects of glucocorticoid analogs and a prostaglandin on the expression of SOST in hMSC cells. hMSC cells were treated with BMP-6 (250 ng/ml) in the absence or presence of dexamethasone (DEX at 10⁻⁷M), tauroursodeoxycholic acid (Tauro at 2×10⁻⁶ M), fluocinolone (Fluo at 10⁻⁷M), lovastatin (Lova at 10⁻⁷M) ICI 182,780 (ICI at 10⁻⁶M), 17β-estradiol (Estrogen at 10⁻⁶M) and prostaglandin E2 (PGE2 at 10⁻⁶M) for 72 hrs. RNA was isolated and analyzed by RT-PCR for SOST. The DAD genie was used as a control for DNA loading. DEX, Fluo and PGE2 blocked the induction of SOST by BMP-6.

FIG. 9A provides chemical structure of glucocorticoid, dexamethasone, that blocks BMP-induced SOST expression.

FIG. 9B provides chemical structure of a glucocorticoid, triamcinolone, that blocks BMP-induced SOST expression.

FIG. 9C provides chemical structure of a glucocorticoid, fluocinolone acetonide, that blocks BMP-induced SOST expression.

FIG. 9D provides chemical structure of a bile salt, ursodeoxycholic acid, that blocks BMP-induced SOST expression.

FIG. 9E provides chemical structure of an eicosanoid, prostaglandin E2, that blocks BMP-induced SOST expression.

FIG. 10 provides a comparison of the effects of human sclerostin and mouse noggin proteins on alkaline phosphatase (ALP) activity in differentiating human MSC cells. ALP activity is a phenotypic marker for osteoblast differentiation. Human MSC cells were cultured for 7 days in Osteoblast-Inducing media containing noggin (1 or 5 μg/ml) or partially-purified sclerostin protein (1 or 5 μg/ml). Cells were then harvested and analyzed for ALP activity. After 7 days of treatment, mouse noggin at 1 μg/ml had no effect on ALP activity, whereas mouse noggin at 5 μg/ml significantly increased ALP activity (p<0.001 to vehicle-treated cells). Under the same conditions, partially purified preparations of sclerostin consistently decreased ALP activity when administered at either 1 or 5 μg/ml.

FIG. 11 illustrates that human sclerostin also decreased alkaline phosphatase activity in primary cultures of human osteoblasts. Primary human osteoblasts were grown in regular growth media or in Inducing media (to promote differentiation) and then treated with Sclerostin (20 μg/ml) or Control (protein purified from Sf9 conditioned media) for 7 days prior to histochemical staining for alkaline phosphatase activity. Osteoblasts grown in regular growth media expressed low, basal levels of ALP (“No Treatment,” far right panel). These levels increased significantly when cells were grown in Inducing media (fourth panel, purple stain). When a similar group of cells were treated with sclerostin, there was a marked decrease in the amount of ALP expressed, as evidenced by the reduction in purple stain (third panel, “Sclerostin+Inducing Media”).

FIG. 12A illustrates that human sclerostin decreases alkaline phosphatase activity in hMSC cells in a dose-dependent manner. hMSC cells were plated in Osteoblast-Inducing media. Partially-purified sclerostin protein or proteins purified from Sf9 conditioned media (control) were added the next day. Cultures were maintained for 7 days prior to analysis for alkaline phosphatase activity. As illustrated, increasing concentrations of sclerostin give rise to decreasing levels of alkaline phosphatase activity.

FIG. 12B illustrates that human sclerostin decreases mineralization (calcium deposition) in hMSC cells in a dose-dependent manner. hMSC cells were plated in Osteoblast-Inducing media. Partially-purified sclerostin protein or proteins purified from Sf9 conditioned media (control) were added the next day. Cultures were maintained for 8 days, treated with sclerostin or control proteins and maintained for another 13 days before testing for mineralization. As illustrated, increasing concentrations of sclerostin give rise to diminished mineralization.

FIG. 13 illustrates that partially purified preparations of human sclerostin reduce the synthesis of type I collagen by about 50% in cells treated with 10 μg/ml of sclerostin (p<0.001 to control). hMSC cells were cultured in Osteoblast-Inducing media and treated with partially-purified sclerostin protein or proteins purified from Sf9 conditioned media (Control) for 21 days. Sclerostin or Control at the indicated concentrations was added 8 days after plating.

FIG. 14 illustrates that human sclerostin protein decreases expression of osteoblastic markers in cultures of differentiating hMSC cells. hMSC cells were plated in Osteoblast-Inducing media. After 3 days, partially purified sclerostin protein (10 μg/ml) or proteins purified from Sf9 conditioned media (control) were added. Cells were harvested after 40 hrs and RNA was prepared for RT-PCR analyses of osteoblastic markets. As can be seen, RNA levels of markers for adipocytes (PPARγ2) or undifferentiated mesenchymal cells (endoglin) were not affected by treatment with partially purified preparations of sclerostin protein. On the other hand, RNA levels for osteoblast phenotypic markers such as PTHr, Type I collagen, BMP-2 and BMP-6 were significantly reduced in cells treated with partially purified preparations of sclerostin protein compared to cells treated with control.

FIG. 15 illustrates that human sclerostin blocks BMP-6-stimulated activity as well as basal alkaline phosphatase activity in cultures of hMSC. Human MSC were plated in osteoblast-inducing media and treated with vehicle or BMP-6 (500 ng/ml) as well as increasing concentrations of human sclerostin-Flag protein. BMP-6 increased alkaline phosphatase activity. Sclerostin decreased BMP-induced alkaline phosphatase activity as well as basal levels of alkaline phosphatase activity in a dose dependent manner (p<0.0001).

FIG. 16 illustrates that BMP-6 reverses the inhibitory effect of sclerostin on alkaline phosphatase in cultures of hMSC. hMSC were plated in osteoblast-inducing media and treated with sclerostin (10 μg/ml) and increasing amounts of BMP-6. While sclerostin decreased basal levels of ALP, BMP-6 reversed this effect in a dose-dependent manner (p<0.001).

FIGS. 17A-17D illustrate that human sclerostin decreases alkaline phosphatase activity in mouse mesenchymal cells. Mouse mesenchymal C3H10T1/2 cells having ATCC Deposit No. CCL-226 were plated in regular growth media. Human sclerostin, sclerostin immuno-depleted with an anti-Flag M2 antibody and mouse noggin were pre-incubated with 500 ng/ml BMP-6 for 1 hr prior to addition to cells. Cells were then incubated for 72 hrs with the BMP-6, sclerostin, immuno-depleted sclerostin or noggin and tested for alkaline phosphatase activity. The stimulatory effect of BMP-6 (FIG. 17A) on alkaline phosphatase activity in the C3H10T1/2 cells was antagonized by noggin (FIG. 17B) and by sclerostin. To verify the specificity of the sclerostin response (FIG. 17C), sclerostin protein that had been synthesized with a Flag-tag was immuno-depleted by pre-treatment with an anti-Flag M2 antibody/agarose complex prior to addition to the cells. As can be seen in FIG. 17D, pre-treatment of the sclerostin preparation with an anti-Flag antibody completely abolished the antagonism of BMP-6 in the C3H10T1/2 cells, indicating that a sclerostin-specific response exists.

FIG. 18 provides a model of sclerostin activity. Bone morphogenetic proteins enhance the osteoblastic phenotype in osteoprogenitor cells by increasing the expression of osteoblastic markers (ALP, Collagen). Bone morphogenetic proteins also increase SOST levels. However, SOST feeds back to decrease Bone morphogenetic protein levels, resulting in decreased expression of osteoblastic markers. Steroids such as dexamethasone (and possibly estrogen, or androgen) bind to nuclear receptors (HR) and interact with the transcriptional machinery to reduce the production of SOST and therefore decrease sclerostin activity.

FIG. 19 illustrates screening assays provided by the invention for identifying factors that may down-regulate SOST expression. In both assays, the premise is that compounds bind to glucocorticoid receptor (GR) and interact with the BMP machinery to down-regulate activity of the SOST promoter, resulting in less SOST being transcribed. An example of a control compound is dexamethasone (DEX). In Scenario A, bone cells that are responsive to bone morphogenetic proteins and to glucocorticoids may be used to screen chemical libraries for compounds that would block the BMP-induced increase in SOST expression as measured by RT-PCR assays for SOST expression. Compounds selected to be of interest would be those that decrease the expression of SOST. In Scenario B, cultured cells that had been transfected with a DNA construct may be used to screen chemical libraries of compounds. The DNA construct is comprised of the SOST promoter sequence, a glucocorticoid response element (GRE) and a detectable marker (such as luciferase), for example, the DNA construct would have the structure:

-   -   GRE-SOST promoter-Luciferase         Compounds selected to be of interest would be those that         decrease the expression of this DNA construct. Successful         candidates from these screening assays can be tested in         mesenchymal or osteoblastic cells to see if they can block         endogenous sclerostin expression and/or increase osteoblastic         activity in treated cells.

FIG. 20 graphically illustrates that exposure to increasing amounts of human sclerostin decreases the viability of hMSC cells. hMSC cells were plated in Osteoblast-Inducing media and treated with baculo-expressed partially purified preparation of Sclerostin or proteins purified from Sf9 conditioned media (control) for 1 week. Sclerostin and Control were refreshed with each media change. After one week, cells were lysed and processed with Promega's CellTiterGlo Viability assay to detect what percentage of cells were viable. The viability of control and sclerostin-treated cells is plotted on the y-axis as the percentage of signal from vehicle-treated cells.

FIG. 21 shows that sclerostin, but not other BMP antagonists, increases the apoptosis of hMSC. hMSC were plated in osteoblast-inducing media and treated with 20 μg/ml sclerostin, inactivated sclerostin or one the BMP antagonists noggin, chordin, gremlin and twisted gastrulation (Tsg). Caspase activity was used as a measure of apoptosis. Sclerostin increased caspase activity whereas an inactive preparation of sclerostin or the BMP antagonists had no significant effect on caspase activity.

FIG. 22A graphically illustrates that exposure to increasing amounts of human sclerostin increases the apoptosis of hMSC cells in a dose-dependent manner. The amount of caspase activity was used as a measure of apoptosis. hMSC cells were plated in Osteoblast-Inducing media and treated with the indicated amounts of a partially purified preparation of sclerostin or proteins purified from Sf9 conditioned media (control) for 24 hrs. As shown, increasing amounts of sclerostin lead to increased caspase activity.

FIG. 22B graphically illustrates that exposure to increasing amounts of human sclerostin increases the apoptosis of hMSC cells in a dose-dependent manner. The amount of histone-DNA fragments as determined by ELISA (Roche) was used as a measure of apoptosis. hMSC cells were plated in Osteoblast-Inducing media and treated with the indicated amounts of a partially purified preparation of sclerostin or proteins purified from Sf9 conditioned media (control) for 24 hrs. As shown, increasing amounts of sclerostin lead to greater amounts of histone-DNA fragments.

FIG. 23 illustrates that hMSC cells exposed to human sclerostin undergo apoptosis, as detected by Tunel staining for apoptotic nuclei. In contrast, hMSC cells exposed to vehicle or conditioned media show little evidence of apoptosis. hMSC cells were plated in Osteoblast-Inducing media and treated with a partially purified preparation of Sclerostin (20 μg/ml), proteins purified from Sf9 conditioned media (Control), or dexamethasone (DEX, 1 μM, positive control) for 24 hrs. Tunel staining for apoptotic nuclei (arrows point to positively stained nuclei) was performed using Roche's In Situ Cell Death Detection kit. Magnification, Bright field, 100×.

FIG. 24A shows the time course of effect of human sclerostin on the apoptosis of hMSC cells. hMSC cells were plated in Osteoblast-Inducing Media and treated with sclerostin. Cells were harvested and assayed for caspase activity at the indicated times. Caspase activity remained elevated 72 hrs after treatment of hMSC cells with sclerostin.

FIG. 24B illustrates that rat sclerostin also induced the apoptosis of hMSC cells. Human MSC cells were plated in Osteoblast-Inducing media and treated with human sclerostin or rat sclerostin for 24 hrs prior to assay for caspase activity (Roche).

FIG. 25 shows that commercially available inhibitors of caspase activity can block the sclerostin-induced apoptosis of hMSC cells. hMSC cells were plated in Osteoblast-Inducing media and treated with human sclerostin or proteins purified from Sf9 conditioned media (Control), in the presence or absence of caspase inhibitors for 24 hrs. Caspase activity was determined by Roche ELISA. Caspase inhibitors (Cas-1, Cas-3, Calbiochem) alone or in combination with each other efficiently blocked the sclerostin-induced increase in caspase activity. Caspase inhibitors also blocked caspase activity induced by rat sclerostin in these cells.

FIG. 26 provides a schematic diagram illustrating how sclerostin may induce apoptosis in maturing osteoblast cells. Mesenchymal cells develop along a defined temporal pathway from inducible progenitor cells to mature osteoblasts and finally, into lining cells or osteocytes. As these cells progress, they express phenotypic markers characteristic of each stage of differentiation (e.g. type I collagen for pre-osteoblasts, mineralization for mature osteoblasts). Sclerostin is highly expressed by maturing osteoblasts. Sclerostin regulates mineralization and hence bone formation by a negative feedback mechanism. Sclerostin decreases osteoblastogenesis by increasing the apoptosis of cells at early stages of osteoblast differentiation. Signals from osteocytes/lining cells regulate this entire process. Sclerostin may be an integral connection for osteocytic regulation of bone remodeling.

FIG. 27 provides one possible assay for sclerostin antagonists. In this assay, a variety of cells may be tested separately. In one assay, immortalized or transformed bone cells can be cultured in the presence of sclerostin and a test compound or test sample. In another assay, primary osteoblastic or mesenchymal cells that can be induced to differentiate are exposed to a test compound or test sample. After a period of incubation, apoptosis is measured. Factors that reduce apoptosis are candidate sclerostin antagonists that can be further characterized in a number of ways as illustrated herein.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides compositions and methods for modulating bone density in a mammal. In particular, the invention provides factors that diminish SOST expression and antagonists of the SOST gene product, sclerostin. According to the invention, sclerostin decreases bone mineralization, collagen synthesis and alkaline phosphatase (ALP) activity in maturing bone cells in both direct and indirect ways. One way that sclerostin regulates bone density and bone formation is by acting as an antagonist of bone morphogenetic proteins (BMPs). Another way that sclerostin regulates bone density and formation is through apoptosis of cells involved in bone mineralization and bone formation.

By modulating or diminishing the amount of sclerostin or by inhibiting its action, bone morphogenetic proteins can perform essential functions needed for the commitment and differentiation of osteoprogenitor cells and pre-osteoblastic cells. Moreover, by administering antagonists of sclerostin-mediated apoptosis, the survival and longevity of cells involved in bone mineralization can be increased. Such compositions and procedures provide therapeutic strategies for increasing bone mineralization and formation.

The invention further provides assays for identifying factors that diminish SOST expression and/or antagonists that counteract the effects of sclerostin.

Bone Cell Development

A small population of pluripotent mesenchymal/stromal cells, called inducible osteoprogenitor cells, can be induced to differentiate into osteoblastic cells (Pittenger, M E et al. 1999). These inducible osteoprogenitor cells develop and express certain phenotypic markers in a defined, sequential manner (Pockwinise et al. 1992; Lian et al. 1999). Osteoprogenitor cells express type I collagen whereas committed pre-osteoblasts and osteoblasts express many of the phenotypic markers that are typically identified with a cell of the osteoblast lineage. These markers include type I collagen, alkaline phosphatase, parathyroid hormone receptor (PTHr) and osteopontin. In the terminal stage of osteoblast differentiation, osteocytes are surrounded by deposits of mineral as well as matrix proteins such as CD44 and osteocalcin. Therefore, the development, growth and differentiation of osteoblastic precursor cells into mature osteoblasts occur in a defined, time-dependent manner (Pockwinse et al., 1992).

The expression of phenotypic markers that are characteristic of osteoblasts at different stages of differentiation is regulated by a variety of factors, including the bone morphogenetic proteins (BMPs). It is thought that BMP-6 may initiate osteoblast differentiation at an early osteoprogenitor stage but that other bone morphogenetic proteins or growth factors may be necessary to continue the differentiation process (Gitelman et al., 1995; Boden et al., 1997). Certain studies indicate that BMP-2 and BMP-4 are needed for the commitment and differentiation of osteoprogenitor and pre-osteoblastic cells to osteoblasts (Katagiri et al., 1990; Oreffo et al. 1999; Suzawa et al., 1999).

Antagonists of bone morphogenetic proteins, for example, noggin, gremlin, chlordin and the Dan/cereberus family of proteins, have also been identified. However, the role that bone morphogenetic protein antagonists play in the regulation and modulation of bone morphogenetic protein action in osteoblastic cells is not well understood.

SOST and Sclerostin

The sequence of the human SOST gene is approximately 22 kb and can be found as Genbank Accession No. AF326736 in the NCBI nucleotide database (SEQ ID NO:1). See website at ncbi.nlm.nih.gov/Genbank/GenbankOverview. Co-owned and co-assigned U.S. Pat. Nos. 6,395,511 and 6,489,445, incorporated by reference herein, provide additional sequence information and a further description of the properties of the SOST gene and its gene product (called beer therein).

The human SOST cDNA has Genbank Accession No. NM025237, and is provided for the convenience of the reader as follows (SEQ ID NO:2).

1 AGAGCCTGTG CTACTGGAAG GTGGCGTGCC CTCCTCTGGC 41 TGGTACCATG CAGCTCCCAC TGGCCCTGTG TCTCGTCTGC 81 CTGCTGGTAC ACACAGCCTT CCGTGTAGTG GAGGGCCAGG 121 GGTGGCAGGC GTTCAAGAAT GATGCCACGG AAATCATCCC 161 CGAGCTCGGA GAGTACCCCG AGCCTCCACC GGAGCTGGAG 201 AACAACAAGA CCATGAACCG GGCGGAGAAC GGAGGGCGGC 241 CTCCCCACCA CCCCTTTGAG ACCAAAGACG TGTCCGAGTA 281 CAGCTGCCGC GAGCTGCACT TCACCCGCTA CGTGACCGAT 321 GGGCCGTGCC GCAGCGCCAA GCCGGTCACC GAGCTGGTGT 361 GCTCCGGCCA GTGCGGCCCG GCGCGCCTGC TGCCCAACGC 401 CATCGGCCGC GGCAAGTGGT GGCGACCTAG TGGGCCCGAC 441 TTCCGCTGCA TCCCCGACCG CTACCGCGCG CAGCGCGTGC 481 AGCTGCTGTG TCCCGGTGGT GAGGCGCCGC GCGCGCGCAA 521 GGTGCGCCTG GTGGCCTCGT GCAAGTGCAA GCGCCTCACC 561 CGCTTCCACA ACCAGTCGGA GCTCAAGGAC TTCGGGACCG 601 AGGCCGCTCG GCCGCAGAAG GGCCGGAAGC CGCGGCCCCG 641 CGCCCGGAGC GCCAAAGCCA ACCAGGCCGA GCTGGAGAAC 681 GCCTACTAGA GCCCGCCCGC GCCCCTCCCC ACCGGCGGGC 721 GCCCCGGCCC TGAACCCGCG CCCCACATTT CTGTCCTCTG 761 CGCGTGGTTT GATTGTTTAT ATTTCATTGT AAATGCCTGC 801 AACCCAGGGC AGGGGGCTGA GACCTTCCAG GCCCTGAGGA 841 ATCCCGGGCG CCGGCAAGGC CCCCCTCAGC CCGCCAGCTG 881 AGGGGTCCCA CGGGGCAGGG GAGGGAATTG AGAGTCACAG 921 ACACTGAGCC ACGCAGCCCC GCCTCTGGGG CCGCCTACCT 961 TTGCTGGTCC CACTTCAGAG GAGGCAGAAA TGGAAGCATT 1001 TTCACCGCCC TGGGGTTTTA AGGGAGCGGT GTGGGAGTGG 1041 GAAAGTCCAG GGACTGGTTA AGAAAGTTGG ATAAGATTCC 1081 CCCTTGCACC TCGCTGCCCA TCAGAAAGCC TGAGGCGTGC 1121 CCAGAGCACA AGACTGGGGG CAACTGTAGA TGTGGTTTCT 1161 AGTCCTGGCT CTGCCACTAA CTTGCTGTGT AACCTTGAAC 1201 TACACAATTC TCCTTCGGGA CCTCAATTTC CACTTTGTAA 1241 AATGAGGGTG GAGGTGGGAA TAGGATCTCG AGGAGACTAT 1281 TGGCATATGA TTCCAAGGAC TCCAGTGCCT TTTGAATGGG 1321 CAGAGGTGAG AGAGAGAGAG AGAAAGAGAG AGAATGAATG 1361 CAGTTGCATT GATTCAGTGC CAAGGTCACT TCCAGAATTC 1401 AGAGTTGTGA TGCTCTCTTC TGACAGCCAA AGATGAAAAA 1441 CAAACAGAAA AAAAAAAGTA AAGAGTCTAT TTATGGCTGA 1481 CATATTTACG GCTGACAAAC TCCTGGAAGA AGCTATGCTG 1521 CTTCCCAGCC TGGCTTCCCC GGATGTTTGG CTACCTCCAC 1561 CCCTCCATCT CAAAGAAATA ACATCATCCA TTGGGGTAGA 1601 AAAGGAGAGG GTCCGAGGGT GGTGGGAGGG ATAGAAATCA 1641 CATCCGCCCC AACTTCCCAA AGAGCAGCAT CCCTCCCCCG 1681 ACCCATAGCC ATGTTTTAAA GTCACCTTCC GAAGAGAAGT 1721 GAAAGGTTCA AGGACACTGG CCTTGCAGGC CCGAGGGAGC 1761 AGCCATCACA AACTCACAGA CCAGCACATC CCTTTTGAGA 1801 CACCGCCTTC TGCCCACCAC TCACGGACAC ATTTCTGCCT 1841 AGAAAACAGC TTCTTACTGC TCTTACATGT GATGGCATAT 1881 CTTACACTAA AAGAATATTA TTGGGGGAAA AACTACAAGT 1921 GCTGTACATA TGCTGAGAAA CTGCAGAGCA TAATAGCTGC 1961 CACCCAAAAA TCTTTTTGAA AATCATTTCC AGACAACCTC 2001 TTACTTTCTG TGTAGTTTTT AATTGTTAAA AAAAAAAAGT 2041 TTTAAACAGA AGCACATGAC ATATGAAAGC CTGCAGGACT 2081 GGTCGTTTTT TTGGCAATTC TTCCACGTGG GACTTGTCCA 2121 CAAGAATGAA AGTAGTGGTT TTTAAAGAGT TAAGTTACAT 2161 ATTTATTTTC TCACTTAAGT TATTTATGCA AAAGTTTTTC 2201 TTGTAGAGAA TGACAATGTT AATATTGCTT TATGAATTAA 2241 CAGTCTGTTC TTCCAGAGTC CAGAGACATT GTTAATAAAG 2281 ACAATGAATC ATGACCGAAA GAAAAAAAAA AAAAAAAAAA 2321 AAA

The SOST gene gives rise to the sclerostin protein. The human sclerostin protein has Genbank Accession No. NP079513 and is provided below for convenient reference as SEQ ID NO:3.

1 MQLPLALCLV CLLVHTAFRV VEGQGWQAFK NDATEIIPEL 41 GEYPEPPPEL ENNKTMNRAE NGGRPPHHPF ETKDVSEYSC 81 RELHFTRYVT DGPCRSAKPV TELVCSGQCG PARLLPNAIG 121 RGKWWRPSGP DFRCIPDRYR AQRVQLLCPG GEAPRARKVR 161 LVASCKCKRL TRFHNQSELK DFGTEAARPQ KGRKPRPRAR 201 SAKANQAELE NAY

The promoter for the human SOST gene is found within nucleotides 7960-11960 of SEQ ID NO:1. This promoter sequence is provided below as SEQ ID NO:4.

7960 T 7961 GAATGCCACA GCTTGTCAGC AGCCAGCAGA AGGCAGGTAA 8001 AAGGCCTTCC TCACTGTCCT CGAAGGAACC AACTCTGCCA 8041 ATGTCTTGAA CTTGCACTCC TAACCTCCAG CTCTGTGAGA 8081 CGACTTCTGT TGTTTATGCC ACCCAATTTG TGGTACTTAG 8121 TTACGGCAGC CTCATCAAAG TACCACCTAT GGGAGCCTCT 8161 ATTTTGCAGG TGAGGGCGGG GACTGGGCTG AGTTTTCTGG 8201 AAAACAGCCC TGCAATACCC TCATCAGACC ACCAAACTCT 8241 TCACACTCCC TCAGACACAG CATTCACTTC CAGAAATAAC 8281 TCTAAAGTTT TGTTTTGTTT TTTTAAACTT TGTGGAATAC 8321 TACTCAGCCA AAAAAAAAAA AAAAGAAAAG AAAAAGGAAC 8361 ATGTTACTGA TATGTACAAC TTGGATAATG GAAATAATGC 8401 TGAGTGAAAA AAAAATCCCC AAAGGCTACA TACTAATTGA 8441 TTCCATTTAT ATAACCTTTT TTTTTTTTTT TTGAGACAGT 8481 CTCACTCTGT CACCCAGGCT GGAGCACAGT GGCGCGATCT 8521 CAGCTCACTG CAACTTCCGC CTCCTGAGTT CAAGCGATTC 8561 TCTTGCCTTA GCTTCCCAAG TAGCTGGGAT TACAGGTGCG 8601 TGCCACCATG CCCAGCTAAT TTTTGTATTT TTAGTAGAGA 8641 CAGGGTTTCG CCATGTTGGC CAGGCTGGTC TCGAACTCCT 8681 GACCTCAAGT GATCTGCCTG CCTTGGCTTC CCAAAGTGCT 8721 GGGATTACAT GAGTGAGCCA CCGCACCTGG TCGCATTTAT 8761 GTAACAATTT TGAAGTGAAA AAAAAAATGA CAGAAATGGA 8801 GATTAGATGA GTAGTTGCCA GGGGTTAGTT GTGGGAGGGA 8841 GGGAAAAGGA GGGAAGGAGG TGGGCAACAG GAGAAAGACT 8881 TGTGGTCACA GAGCTGTGCT TTATCTTGAC TGTGGTGGAT 8921 CCCCAAATTT ACCCGTGACA AGATTGCATA GAACTAAGTA 8961 TACACACACG TGAATGCGTG TGCACGCACA CAGTAGAGGT 9001 TAAGCCACGG GAGATGTGGG TAAGATTGGT AAATTGTGTC 9041 AATATCAATA TCCTAGTTGT GATATTGTCC TATAGTTTCG 9081 CAAGGTGTTA TTGTTGTGGG AAACTGGATA AAGGATACAC 9121 GGAGTCTGCA TTTTCTTTTT TTTATTTTTA TTTTTTGAGA 9161 CGGGGTCTCA CTCTGTCAAC CAGGCTGGAG TGCAGTGGCC 9201 CAAGTATGGC TCACTGCAGC CTCGACCTCA ACCTCAAGTG 9241 AACCTCCCAC CTCAGCCTCC CAAGTAGCTA AGACCACAGG 9281 CGTGCGACCC CATGCCCAGC TAATTTTTAA ATTTTTTGTA 9321 GAGACTAGGC CTCACCATGT TGCCCAGGCT TTTATTTCTT 9361 ATAAGTATAT TTAAATTTAT AATTATATCC ACATTTTAAA 9401 ATTTTAATTT AAAAAATTAC TCTGAGGCCG GGCATTGTGG 9441 CTCATGCCTC TAATCCCCAG CACCTTGGGA GGCCGAGTTG 9481 GGCAGATCAC CCGAGGTCAG AAGTTCGAGA CCAGCCTGAG 9521 TAACATGGAG AAACCCCCGT CTCTACTAAA AATACAAAAT 9561 TGGCCGGGCG TGGTGGTGCA TTCCTGTAAT CCCAGCTACT 9601 CGGGAGGCTG AGGCAGGAGA ATTGCTTGAA CCCAGGAGGT 9641 GGAGGTTGCA GTGAGCCAAG ATTGTGCCAC TGCACTGCAG 9681 CCTGGGCCAC AGAGAGAATC TGCCAAAAAA AGAAAAAAAA 9721 AAAAATTTCA GCCGTACAAG GATGTTCATA GCAACCCTGC 9761 TGGAAATAGG AAAAAAAATT GGAAATAACC TAAACTACTC 9801 ACAATAGGAA TCAGCTAAAA CCCTGGGGGT TTAATTCCAG 9841 GGAATACTGT GAACAATGAC AAGTTTGTGG ACTGAGTAAA 9881 AATAAACAGC TGTCAATGAC TTAACATTAA ATGAAACAGC 9921 AGAAGATGTC ACAGCAGGTT CTCGCTGAGC CATTCAGAGG 9961 GGTGTGGATC ATTTAGAGGT TCAAGTCCAC TGGATTCTTC 10001 TTTTTCCTTT TAATATTACT TCACTTCCAA ATAAGGAAAG 10041 GAAAGGAAAG GAAATCACGT CCAGTCCTGA GACTTGCCAT 10081 CCTGCAGTCA CCCCTCCTTT TGTCTCCAGC AGGTGGCAGA 10121 CGCGTTCCAG GGATGAATCC CACTGCCTCT GTTTAATGCA 10161 GACGGTCCAG CCGCTCCCAA CAGCAGGTGG GGCTATAAGC 10201 ATCCATCCTA CCTGCTCAAG GAACCCAGGC ATCAGAACTG 10241 CTCTCTCCCA AGTCCATTGC AAGAAGGCAG TCGTCTGGTC 10281 ATGAGAGGGT TAACAGTCCA CATTCCAGAG CAAGGGAAAA 10321 GGAGGCTGGA GGGTCATAGA CAAGGGGAGG TGGTGCGGAG 10361 GGCCAGCTTC TCACAACACT ACCGGCTCTG CTGGGAGAGA 10401 TAGATCACCC CCAACAATGG CCACAGCTGT TTTCATCTGC 10441 CCTGAAGGAA ACTGACTTAG GAAGCAGGTA TCAGAGAGGG 10481 CCCTTCCTGA GGGGGCTTCT GTCTGGCTTG TAAAACTGTC 10521 AGAGCAGCTG CATTCATGTG TCGGATGATG GATGATGGAA 10561 AGGACAGTCG GCTGCAGATG GACACAGCGA CTTGCAAGTT 10601 GAGGCAGGTG GCAAAGGACT TGCAGAGGCT CTGCAGGTGG 10641 GGCATGCTGA TTCATTGCCC AGTTAAAATA CCAGAGGATC 10681 TGGGCAGCCT CTTCACAGGA GCTGCTTGTC CTCAAACAAT 10721 CTGTCTTCAA TGAAAGATTC CTCTGGCCTT CCTTTCTCTT 10761 CTTGCACCTC AGGTGTGAAT CCTTCTCCCC CACGCCTCTA 10801 CCTGCGCCCC CGCCCCCCGC CCCGGCCCTG TGTGGCTCAT 10841 TATATGCAGG GCCAAGGCAG CATTTTCTCT TAGCTTCTTT 10881 GTGACCAGTT GGTCCTGGGA TGGCTTCATG GAACACATCC 10921 TGTGGTGTGC ACCAATGAAG CTTTCCATAC AGGACTCAAA 10961 ACTGTTTTTG AAAAATGTAA CCAGCTGGAA GACAAGAAAA 11001 TAAAATGTCA GCACTAAAAA CGCTGGCTGT GGCTTTTGCT 11041 AAGGAAAGGA ATTTGGTGTT GTCTTCTCAC ACACACAGAC 11081 TGGTTGGGGA AATGACTGTC TTCAGCACAT CACCCTGCGA 11121 GCCACAGTGA GTGCCCTGGC TCAGAAGTGC CTGTCACAGT 11161 GCACAGGATC CCTGAGGAGC ATGAGCTGGG ATTTCCTCTG 11201 TGCTGTCCAT CACAGGAGCC TGAGTGACCA GCGCATCCTC 11241 GATTTGTAAC CAGAATCCTG CCCTCTCTCC CAAGCGGGCA 11281 CCCTTGCTCT GACCCTCTAG TTCTCTCTCT TGCCTTCCAG 11321 AGAATACCAA GAGAGGCTTT CTTGGTTAGG ACAATGAATG 11361 CTGAGACTTG TGGAGTTGGG ACCAATGGGA TTTCTTTAAA 11401 AGCATCTTTT TGCCTCTGGC TGGGTCTATG GGGGTCAAAC 11441 AGAAACACCT TGGGCCATTT GTTGGTGGGG TGACAAATGA 11481 ACTTGGCCTG AGAAATGGAA TAGGCCGGGC TCAGCCCCGC 11521 GAAGCACTCA GAACTGCACA TTTTCTTTGT TGAGCGGGTC 11561 CACAGTTTGT TTTGAGAATG CCCGAGGGCC CAGGGAGACA 11601 GACAATTAAA AGCCGGAGCT CATTTTGATA TCTGAAAACC 11641 ACAGCCGCCA GCACGTGGGA GGTGCCGGAG AGCAGGCTTG 11681 GGCCTTGCCT CACACGCCCC CTCTCTCTGG GTCACCTGGG 11721 AGTGCCAGCA GCAATTTGGA AGTTTGCTGA GCTAGAGGAG 11761 AAGTCTTTGG GGAGGGTTTG CTCTGAGCAC ACCCCTTTCC 11801 CTCCCTCCGG GGCTGAGGGA AACATGGGAC CAGCCCTGCC 11841 CCAGCCTGTC CTCATTGGCT GGCATGAAGC AGAGAGGGGC 11881 TTTAAAAAGG CGACCGTGTC TCGGCTGGAG ACCAGAGCCT 11921 GTGCTACTGG AAGGTGGCGT GCCCTCCTCT GGCTGGTACC 11960 ATGCAGCTCC CACTGGCCCT GTGTCTCGTC TGCCTGCTG

The invention can also be practiced with variants of the SOST gene and with variants of the sclerostin protein. For example, the invention can be practiced with the mouse or rat SOST gene or with the mouse or rat sclerostin protein. The mouse SOST cDNA has Genbank Accession No. NM024449, and is provided below as SEQ ID NO:5 for easy reference.

1 ATGCAGCCCT CACTAGCCCC GTGCCTCATC TGCCTACTTG 41 TGCACGCTGC CTTCTGTGCT CTGGAGGGCC AGGGGTGGCA 81 AGCCTTCAGG AATGATGCCA CAGAGGTCAT CCCAGGGCTT 121 GGAGAGTACC CCGAGCCTCC TCCTGAGAAC AACCAGACCA 161 TGAACCGGGC GGAGAATGGA GGCAGACCTC CCCACCATCC 201 CTATGACGCC AAAGATGTGT CCGAGTACAG CTGCCGCGAG 241 CTGCACTACA CCCGCTTCCT GACAGACGGC CCATGCCGCA 281 GCGCCAAGCC GGTCACCGAG TTGGTGTGCT CCGGCCAGTG 321 CGGCCCCGCG CGGCTGCTGC CCAACGCCAT CGGGCGCGTG 361 AAGTGGTGGC GCCCGAACGG ACCGGATTTC CGCTGCATCC 401 CGGATCGCTA CCGCGCGCAG CGGGTGCAGC TGCTGTGCCC 441 CGGGGGCGCG GCGCCGCGCT CGCGCAAGGT GCGTCTGGTG 481 GCCTCGTGCA AGTGCAAGCG CCTCACCCGC TTCCACAACC 521 AGTCGGAGCT CAAGGACTTC GGGCCGGAGA CCGCGCGGCC 561 GCAGAAGGGT CGCAAGCCGC GGCCCGGCGC CCGGGGAGCC 601 AAAGCCAACC AGGCGGAGCT GGAGAACGCC TACTAG

The mouse sclerostin protein has Genbank Accession No. NP077769, and is provided below as SEQ ID NO:6 for easy reference.

1 MQPSLAPCLI CLLVHAAFCA VEGQGWQAFR NDATEVIPGL 41 GEYPEPPPEN NQTMNRAENG GRPPHHPYDA KDVSEYSCRE 81 LHYTRFLTDG PCRSAKPVTE LVCSGQCGPA RLLPNAIGRV 121 KWWRPNGPDF RCIPDRYRAQ RVQLLCPGGA APRSRKVRLV 161 ASCKCKRLTR FHNQSELKDF GPETARPQKG RKPRPGARGA 201 KANQAELENA Y

The rat SOST cDNA has Genbank Accession No. NM030584, and is provided below as SEQ ID NO:7 for easy reference.

1 GAGGACCGAG TGCCCTTCCT CCTTCTGGCA CCATGCAGCT 41 CTCACTAGCC CCTTGCCTTG CCTGCCTGCT TGTACATGCA 81 GCCTTCGTTG CTGTGGAGAG CCAGGGGTGG CAAGCCTTCA 121 AGAATGATGC CACAGAAATC ATCCCGGGAC TCAGAGAGTA 161 CCCAGAGCCT CCTCAGGAAC TAGAGAACAA CCAGACCATG 201 AACCGGGCCG AGAACGGAGG CAGACCCCCC CACCATCCTT 241 ATGACACCAA AGACGTGTCC GAGTACAGCT GCCGCGAGCT 281 GCACTACACC CGCTTCGTGA CCGACGGCCC GTGCCGCAGT 321 GCCAAGCCGG TCACCGAGTT GGTGTGCTCG GGCCAGTGCG 361 GCCCCGCGCG GCTGCTGCCC AACGCCATCG GGCGCGTGAA 401 GTGGTGGCGC CCGAACGGAC CCGACTTCCG CTGCATCCCG 441 GATCGCTACC GCGCGCAGCG GGTGCAGCTG CTGTGCCCCG 481 GCGGCGCGGC GCCGCGCTCG CGCAAGGTGC GTCTGGTGGC 521 CTCGTGCAAG TGCAAGCGCC TCACCCGCTT CCACAACCAG 561 TCGGAGCTCA AGGACTTCGG ACCTGAGACC GCGCGGCCGC 601 AGAAGGGTCG CAAGCCGCGG CCCCGCGCCC GGGGAGCCAA 641 AGCCAACCAG GCGGAGCTGG AGAACGCCTA CTAG

The rat sclerostin protein has Genbank Accession No. NP085073, and is provided below as SEQ ID NO:8 for easy reference.

1 MQLSLAPCLA CLLVHAAFVA VESQGWQAFK NDATEIIPGL 41 REYPEPPQEL ENNQTMNRAE NGGRPPHHPY DTKDVSEYSC 81 RELHYTRFVT DGPCRSAKPV TELVCSGQCG PARLLPNAIG 121 RVKWWRPNGP DFRCIPDRYR AQRVQLLCPG GAAPRSRKVR 161 LVASCKCKRL TRFHNQSELK DFGPETARPQ KGRKPRPRAR 201 GAKANQAELE NAY Other SOST nucleic acids and sclerostin proteins can be used for the practice of the invention, including the vervet SOST cDNA [accession number AF326742] and the bovine SOST cDNA [accession number AF326738].

According to the invention, the expression of the SOST gene increases with the maturation and differentiation of osteoblasts as well as with the onset of mineralization. Hence, SOST expression can be used as a marker for osteoblast differentiation.

However, factors that increase SOST expression lead to decreased bone mineralization because the SOST gene product, sclerostin, is an antagonist of bone morphogenetic proteins and causes apoptosis of osteoblasts. Sclerostin decreased the expression of many phenotypic markers of pre-osteoblasts/osteoblasts (ALP, type I collagen, PTHr) when it was added to cultures of differentiating hMSC cells and primary cultures of osteoblastic cells. Moreover, sclerostin interacted with and antagonized the activity of BMP-6, thereby inhibiting osteoblast differentiation.

According to the invention, sclerostin plays an integral role in the regulation of bone matrix formation and mineralization. Although several proteins are thought to function as antagonists of bone morphogenetic protein action (for example, noggin and gremlin), it appears that when the sclerostin function is lost that function cannot be replaced by noggin or any of the other members of the DAN family of antagonists.

A schematic diagram of how sclerostin to affects bone cell biology is depicted in FIG. 26. Sclerostin exerts its effects on pre-osteoblasts, osteoprogenitor, and mature osteoblasts cells. By depriving pre-osteoblasts and osteoprogenitor cells of factors such as bone morphogenetic proteins, these cells are prevented from completing their differentiation into mature osteoblasts. Thus, fewer osteoblasts are available to provide mineralization. In addition, these proteins play important anti-apoptotic roles, which are potentially impacted by increasing exposure to sclerostin. As a result, alkaline phosphatase activity and synthesis of type I collagen are reduced in pre-osteoblasts and osteoprogenitor cells, while mineralization is affected in mature osteoblasts treated with sclerostin. Reducing the expression of SOST or the amount of sclerostin available to developing osteoblasts permits more cells to progress through differentiation to produce more mature osteoblasts, more synthesis of type I collagen and greater deposition of mineral in bones.

Several factors enhance the expression of SOST, including insulin-like growth factor-1 and bone morphogenetic proteins such as BMP-2, BMP-4, and BMP-6. When bone morphogenetic proteins are present, retinoic acid and vitamin D also enhanced the levels of SOST expression. Such factors can therefore lead to diminished collagen synthesis and less mineralization within bones through increased synthesis of sclerostin.

In contrast, SOST expression levels decrease when dexamethasone is present with BMP-4 or BMP-6. Therefore, dexamethasone tends to abolish the stimulatory effect of BMP-4 and BMP-6 on SOST expression. Other chemical entities including glucocorticoid analogs, bile salts and prostaglandins also modulate the effects of bone morphogenetic proteins on SOST expression, as described below.

Modulating SOST/Sclerostin

According to the invention, any agents that modulate the ability of sclerostin to decrease osteoblastic activity are useful in increasing bone formation, modulating bone resorption and augmenting bone mineralization. Such agents can act directly or indirectly on SOST or sclerostin. Such agents can act at the transcriptional, translational or protein level to modulate the ability of sclerostin to decrease osteoblastic activity.

The term “modulate” or “modulating” means changing, that is increasing or decreasing. Hence, while agents that can decrease SOST expression or sclerostin activity are often used in the compositions and methods of the invention, agents that also increase SOST expression or sclerostin activity are also encompassed within the scope of the invention.

Agents useful for modulating SOST expression and sclerostin activity include, but are not limited to, steroids, alkaloids, terpenoids, peptoids, peptides, nucleic acids, anti-sense nucleic acids and synthetic chemicals. In some embodiments, the SOST antagonist or agonist can bind to a glucocorticoid receptor. For example, dexamethasone tends to abolish the stimulatory effect of BMP-4 and BMP-6 on SOST expression. Other chemical entities including glucocorticoid analogs, bile salts and prostaglandins also modulate the effects of bone morphogenetic proteins on SOST expression.

In one embodiment of the invention, steroids of the formula I can be used for modulating the expression of sclerostin.

wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ are separately carbonyl, halo, fluorine, hydrogen, hydroxyl, lower acyl, lower alkoxy, lower alkyl, or lower hydroxy alkyl. Preferred R₁, R₂, R₃, R₄, R₅, R₆, and R₇ groups are carbonyl, hydroxy, hydrogen, or lower hydroxy alkyl. Preferably, R₁ is carbonyl or hydroxy and R₂ is lower alkyl. Also preferably, R₈ is a fluorine, hydrogen or halo group.

The following general definitions are used, unless otherwise described: halo is fluoro, chloro, bromo, or iodo. Alkyl, alkoxy, alkenyl, alkynyl, etc. denote both straight and branched groups; but reference to an individual radical such as “propyl” embraces only the straight chain radical, a branched chain isomer such as “isopropyl” being specifically referred to. Aryl denotes a phenyl radical or an ortho-fused bicyclic carbocyclic radical having about nine to ten ring atoms in which at least one ring is aromatic. Aryloxy means aryl-O—.

More specifically, lower alkyl means (C₁-C₆) alkyl. Such (C₁-C₆) alkyl can be methyl, ethyl, propyl, isopropyl, butyl, iso-butyl, sec-butyl, pentyl, 3-pentyl, or hexyl. Lower alkoxy generally means (C₁-C₆) alkoxy; such (C₁-C₆) alkoxy can, for example, be methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, pentoxy, 3-pentoxy, or hexyloxy. Preferred lower alkyl groups are (C₁-C₃) alkyl including methyl ethyl, propyl, isopropyl and the like. More preferred lower alkyl groups are methyl. Lower acyl refers to a carbonyl group attached to a lower alkyl group (e.g., —CO—CH₃). Lower hydroxy alkyl refers to a hydroxy group attached to a lower alkyl or lower alkylene group (e.g. —CH₂—CH₂—OH).

One example of an effective SOST/sclerostin antagonist is dexamethasone. Dexamethasone is a synthetic version of the glucocorticoid hormone, cortisol, which has been used as an anti-inflammatory agent. The structure of dexamethasone is provided below.

Cortisol and other glucocorticoids and molecules with structures similar to dexamethasone are also contemplated by the invention as antagonists of sclerostin. Androgens and estrogens are also contemplated as antagonists of sclerostin. Other chemical entities including glucocorticoid analogs, bile salts and prostaglandins also modulate the effects of bone morphogenetic proteins on SOST expression.

Exemplary bile salts can have the following structure:

wherein R₁, R₂, R₃, R₄, R₅, R₆, R₇, and R₈ groups are as described above, and R₉ is carbonyl, halo, fluorine, hydrogen, hydroxyl, lower acyl, lower alkoxy, lower alkyl, or lower hydroxy alkyl. Preferably, R₉ is hydrogen, hydroxyl, lower acyl, lower alkyl, or lower hydroxy alkyl.

Exemplary prostaglandins or eicosanoids can have the following structure:

wherein R₁₀ and R₁₁ are separately carbonyl, halo, fluorine, hydrogen, hydroxyl, lower acyl, lower alkoxy, lower alkyl, lower hydroxy alkyl, aryl or aryloxy.

Compounds or molecules that stimulate the degradation of SOST transcripts or sclerostin can also be used to diminish the levels of sclerostin and enhance bone mineralization.

In another embodiment, the invention provides anti-sense RNA or DNA molecules to modulate SOST expression, sclerostin translation and/or the degradation oft SOST transcripts. For example, an anti-sense RNA or DNA that can hybridize to a nucleic acid having any one of SEQ ID NO:1, 2, 4, 5 or 7 can be used as an anti-sense RNA or DNA for diminishing the expression of sclerostin.

The degradation of SOST mRNA may also be increased upon exposure to small duplexes of synthetic double-stranded RNA through the use of RNA interference (siRNA or RNAi) technology (Scherr, M. et al. 2003; Martinez, L. A. et al. 2002). A process is therefore provided for inhibiting expression of a target gene in a cell. The process comprises introduction of RNA with partial or fully double-stranded character into the cell or into the extracellular environment. Inhibition is specific to SOST RNA because a nucleotide sequence from a portion of the SOST gene is chosen to produce inhibitory RNA. This process is effective in producing inhibition of gene expression.

SiRNAs were designed using the guidelines provided by Ambion (Austin, Tex.). Briefly, the SOST cDNA sequence was scanned for target sequences that had AA dinucleotides. Sense and anti-sense oligonucleotides were generated to these targets (AA+3′ adjacent 19 nucleotides) that contained a G/C content of 35 to 55%. These sequences were then compared to others in the human genome database to minimize homology to other known coding sequences (Blast search).

The target and siRNA sequences designed are provided below.

Target sequence 1: AAGAATGATGCCACGGAAATC (SEQ ID NO:9) Position in gene sequence: 140 GC content: 42.9% Sense strand siRNA: GAAUGAUGCCACGGAAAUCtt (SEQ ID NO:10) Antisense strand siRNA: GAUUUCCGUGGCAUCAUUCtt (SEQ ID NO:11) Target sequence 3: AATGATGCCACGGAAATCATC (SEQ ID NO:12) Position in gene sequence: 143 GC content: 42.9% Sense strand siRNA: UGAUGCCACGGAAAUCAUCtt (SEQ ID NO:13) Antisense strand siRNA: GAUGAUUUCCGUGGCAUCAtt (SEQ ID NO:14) Target sequence 5: AACAACAAGACCATGAACCGG (SEQ ID NO:15) Position in gene sequence: 209 GC content: 47.6% Sense strand siRNA: CAACAAGACCAUGAACCGGtt (SEQ ID NO:16) Antisense strand siRNA: CCGGUUCAUGGUCUUGUUGtt (SEQ ID NO:17) Target sequence 27: AATTGAGAGTCACAGACACTG (SEQ ID NO:18) Position in gene sequence: 950 GC content: 42.9% Sense strand siRNA: UUGAGAGUCACAGACACUGtt (SEQ ID NO:19) Antisense strand siRNA: CAGUGUCUGUGACUCUCAAtt (SEQ ID NO:20) Target sequence 28: AAATGGAAGCATTTTCACCGC (SEQ ID NO:21) Position in gene sequence: 1035 GC content: 42.9% Sense strand siRNA: AUGGAAGCAUUUUCACCGCtt (SEQ ID NO:22) Antisense strand siRNA: GCGGUGAAAAUGCUUCCAUtt (SEQ ID NO:23) Target sequence 30: AAAGTCCAGGGACTGGTTAAG (SEQ ID NO:24) Position in gene sequence: 1093 GC content: 47.6% Sense strand siRNA: AGUCCAGGGACUGGUUAAGtt (SEQ ID NO:25) Antisense strand siRNA: CUUAACCAGUCCCUGGACUtt (SEQ ID NO:26) Target sequence 31: AAGAAAGTTGGATAAGATTCC (SEQ ID NO:27) Position in gene sequence: 1111 GC content: 33.3% Sense strand siRNA: GAAAGUUGGAUAAGAUUCCtt (SEQ ID NO:28) Antisense strand siRNA: GGAAUCUUAUCCAACUUUCtt (SEQ ID NO:29) Target sequence 36: AACTGTAGATGTGGTTTCTAG (SEQ ID NO:30) Position in gene sequence: 1201 GC content: 38.1% Sense strand siRNA: CUGUAGAUGUGGUUUCUAGtt (SEQ ID NO:31) Antisense strand siRNA: CUAGAAACCACAUCUACAGtt (SEQ ID NO:32) Target sequence 40: AATTCTCCTTCGGGACCTCAA (SEQ ID NO:33) Position in gene sequence: 1269 GC content: 47.6% Sense strand siRNA: UUCUCCUUCGGGACCUCAAtt (SEQ ID NO:34) Antisense strand siRNA: UUGAGGUCCCGAAGGAGAAtt (SEQ ID NO:35) Target sequence 47: AAAGAGAGAGAATGAATGCAG (SEQ ID NO:36) Position in gene sequence: 1414 GC content: 38.1% Sense strand siRNA: AGAGAGAGAAUGAAUGCAGtt (SEQ ID NO:37) Antisense strand siRNA: CUGCAUUCAUUCUCUCUCUtt (SEQ ID NO:38) Target sequence 63: AAGAAGCTATGCTGCTTCCCA (SEQ ID NO:39) Position in gene sequence: 1590 GC content: 47.6% Sense strand siRNA: GAAGCUAUGCUGCUUCCCAtt (SEQ ID NO:40) Antisense strand siRNA: UGGGAAGCAGCAUAGCUU (SEQ ID NO:41) Target sequence 70: AAATCACATCCGCCCCAACTT (SEQ ID NO:42) Position in gene sequence: 1726 GC content: 47.6% Sense strand siRNA: AUCACAUCCGCCCCAACUUtt (SEQ ID NO:43) Antisense strand siRNA: AAGUUGGGGCGGAUGUGAUtt (SEQ ID NO:44)

Hence, the invention provides a pharmaceutical composition that includes a carrier and a siRNA comprising SEQ ID NO:11, SEQ ID NO:14, SEQ ID NO:17, SEQ ID NO:20, SEQ ID NO:23, SEQ ID NO:26, SEQ ID NO:29, SEQ ID NO:32, SEQ ID NO:35, SEQ ID NO:38, SEQ ID NO:41 or SEQ ID NO:44, wherein the siRNA can modulate SOST expression. The invention also provides a pharmaceutical composition comprising a carrier and a siRNA that is selectively hybridizable Linder stringent conditions to an RNA derived from a DNA comprising SEQ ID NO:9, SEQ ID NO:12, SEQ ID NO:15, SEQ ID NO:18, SEQ ID NO:21, SEQ ID NO:24, SEQ ID NO:27, SEQ ID NO:30, SEQ ID NO:33, SEQ ID NO:36, SEQ ID NO:39, or SEQ ID NO:42, wherein the siRNA can modulate SOST expression.

Mixtures and combinations of such siRNA molecules are also contemplated by the invention. These compositions can used in the methods of the invention, for example, for treating or preventing apoptosis of bone-related cells or for treating or preventing loss of bone density. These compositions are also useful for modulating (e.g. decreasing) SOST expression.

The siRNA provided herein can selectively hybridize to RNA in vivo or in vitro. A nucleic acid sequence is considered to be “selectively hybridizable” to a reference nucleic acid sequence if the two sequences specifically hybridize one another tinder physiological conditions or tinder moderate stringency hybridization and wash conditions. In some embodiments the siRNA is selectively hybridizable to an RNA (e.g. a SOST RNA) under physiological conditions. Hybridization under physiological conditions can be measured as a practical matter by observing interference with the function of the RNA. Alternatively, hybridization under physiological conditions can be detected in vitro by testing for siRNA hybridization using the temperature (e.g. 37° C.) and salt conditions that exist in vivo.

Moreover, as an initial matter, other in vitro hybridization conditions can be utilized to characterize siRNA interactions. Exemplary in vitro conditions include hybridization conducted as described in the Bio-Rad Labs ZetaProbe manual (Bio-Rad Labs, Hercules, Calif.); Sambrook et al., Molecular Cloning: A Laboratory Manual, 2nd ed., Cold Spring Harbor Laboratory Press, (1989), or Sambrook et al., Molecular Cloning: A Laboratory Manual, 3rd ed., Cold Spring Harbor Laboratory Press, (2001)), expressly incorporated by reference herein. For example, hybridization can be conducted in 1 mM EDTA, 0.25 M Na₂HPO₄ and 7% SDS at 42° C., followed by washing at 42° C. in 1 mM EDTA, 40 mM NaPO₄, 5% SDS, and 1 mM EDTA, 40 mM NaPO₄, 1% SDS. Hybridization can also be conducted in 1 mM EDTA, 0.25 M Na₂ HPO₄ and 7% SDS at 60° C., followed by washing in 1 mM EDTA, 40 mM NaPO₄, 5% SDS, and 1 mM EDTA, 40 mM NaPO₄, 1% SDS. Washing can also be conducted at other temperatures, including temperatures ranging from 37° C. to at 65° C., from 42° C. to at 65° C., from 37° C. to at 60° C., from 50° C. to at 65° C., from 37° C. to at 55° C., and other such temperatures.

The siRNA employed in the compositions and methods of the invention may be synthesized either in vivo or in vitro. In some embodiments, the siRNA molecules are synthesized in vitro using methods, reagents and synthesizer equipment available to one of skill in the art. Endogenous RNA polymerases within a cell may mediate transcription in vivo, or cloned RNA polymerase can be used for transcription in vivo or in vitro. For transcription from a transgene or an expression construct in vivo, a regulatory region may be used to transcribe the siRNA strands.

Depending on the particular sequence utilized and the dose of double stranded siRNA material delivered, the compositions and methods may provide partial or complete loss of function for the target gene (SOST). A reduction or loss of gene expression in at least 99% of targeted cells has been shown for other genes. See, e.g., U.S. Pat. No. 6,506,559. Lower doses of injected material and longer times after administration of the selected siRNA may result in inhibition in a smaller fraction of cells.

The siRNA may comprise one or more strands of polymerized ribonucleotide; it may include modifications to either the phosphate-sugar backbone or the nucleoside. The double-stranded siRNA structure may be formed by a single self-complementary RNA strand or two complementary RNA strands. siRNA duplex formation may be initiated either inside or outside the cell. The siRNA may be introduced in an amount that allows delivery of at least one copy per cell. Higher doses of double-stranded material may yield more effective inhibition.

Inhibition is sequence-specific in that nucleotide sequences corresponding to the duplex region of the RNA are targeted for genetic inhibition. siRNA containing nucleotide sequences identical to a portion of the target gene is preferred for inhibition. However, siRNA sequences with insertions, deletions, and single point mutations relative to the target sequence have also been found to be effective for inhibition. Thus, sequence identity may optimized by alignment algorithms known in the art and calculating the percent difference between the nucleotide sequences. Alternatively, the duplex region of the RNA may be defined functionally as a nucleotide sequence that is capable of hybridizing with a portion of the target gene transcript.

The siRNA may be directly introduced into the cell (i.e., intracellularly); or introduced extracellularly into a cavity, interstitial space, into the circulation of an organism, introduced orally, or may be introduced by bathing an organism in a solution containing siRNA. Methods for oral introduction include direct mixing of siRNA with food of the organism, as well as engineered approaches in which a species that is used as food is engineered to express an siRNA, then fed to the organism to be affected. Physical methods of introducing nucleic acids include injection directly into the cell or extracellular injection into the organism of an siRNA solution.

The siRNA may also be delivered in vitro to cultured cells using transfection agents available in the art such as lipofectamine or by employing viral delivery vectors such as those from lentiviruses. Such in vitro delivery can be performed for testing purposes or for therapeutic purposes. For example, cells from a patient can be treated in vitro and then re-administered to the patient.

The advantages of using siRNA include: the ease of introducing double-stranded siRNA into cells, the low concentration of siRNA that can be used, the stability of double-stranded siRNA, and the effectiveness of the inhibition. The ability to use a low concentration of a naturally-occurring nucleic acid avoids several disadvantages of anti-sense interference.

An antagonist or agonist for sclerostin may also be a co-factor, such as a protein, peptide, carbohydrate, lipid or small molecular weight molecule, which interacts with sclerostin to regulate its activity. Other molecules contemplated as agents for modulating sclerostin include antibodies targeted against sclerostin as well as molecules, compounds or peptides that mimic bone morphogenetic proteins in structure and that bind to and form inactive complexes with sclerostin. Potential polypeptide antagonists include antibodies that react with sclerostin.

As described herein, sclerostin is involved in controlling formation of mature osteoblasts, the primary cell type implicated in bone mineralization. A decrease in the rate of bone mineralization can lead to various bone disorders collectively referred to as osteopenias, including bone disorders such as osteoporosis, osteomyelitis, hypercalcemia, osteopenia brought on by surgery or steroid administration, Paget's disease, osteonecrosis, bone loss due to rheumatoid arthritis; periodontal bone loss, immobilization, prosthetic loosing and osteolytic metastasis.

According to the invention, agents that modulate the function of sclerostin, or that modulate the expression of SOST, can be used to treat any of these diseases. Preferably, SOST/sclerostin antagonists or agents that decrease the function of SOST or sclerostin are used to treat osteoporosis, frail bone problems and related diseases where bone density is inadequate.

Conversely, an increase in bone mineralization can lead to osteopetrosis, a condition marked by excessive bone density. According to the invention, sclerostin may be used to treat conditions characterized by excessive bone density. The most common condition is osteopetrosis in which a genetic defect results in elevated bone mass and is usually fatal in the first few years of life. Osteopetrosis is preferably treated by administration of sclerostin.

The therapeutic methods for treating or preventing a bone disorder such as an inadequate rate of bone mineralization involve administering an agent that can modulate SOST (e.g. a SOST antagonist) to a mammal affected with the bone disorder. Any of the agents or antagonists described herein, or isolated by the methods provided herein, can be administered. Any bone disorder involving diminished mineralization can be treated or prevented using these methods.

The therapeutic methods for treating or preventing a bone disorder such as an excessive bone density involve administering a therapeutically effective amount of sclerostin to a mammal affected with the bone disorder. Any of the available mammalian sclerostin polypeptides (for example, those described herein) can be administered for treating or preventing excessive bone density.

Methods of Isolating Agents that can Modulate SOST/Sclerostin

The invention further provides screening assays that are useful for generating or identifying therapeutic agents for the treatment of bone disorders. In particular, the SOST nucleic acids and sclerostin proteins identified herein may be used in a variety of assays for detecting SOST and/or sclerostin and for identifying factors that interact with SOST nucleic acids or with the sclerostin protein.

In general, an assay for identifying sclerostin involves incubating a test sample tinder conditions which permit binding of sclerostin to a reporter molecule, and measuring the extent of binding. A reporter molecule can be any molecule that stably binds to sclerostin and that can be detected. For example, the reporter molecule can be an anti-sclerostin antibody that is labeled with radioactive isotopes (¹²⁵I, ³²P, ³⁵S, ³H), fluorescent dyes (fluorescein, rhodamine), enzymes and the like. It is understood that the choice of a reporter molecule will depend upon the detection system used.

Sclerostin may be purified or present in mixtures, such as in cultured cells, tissue samples, body fluids or culture medium. Assays may be developed that are qualitative or quantitative, with the latter being useful for determining the binding parameters (affinity constants and kinetics) of the reporter molecule to sclerostin and for quantifying levels of sclerostin in mixtures. Assays may also be used to detect fragments, analogs and derivatives of sclerostin and to identify new sclerostin family members.

Binding assays may be carried out in several formats, including cell-based binding assays, solution-phase assays and immunoassays. In general, test samples or compounds are incubated with sclerostin test samples for a specified period of time followed by measurement of the reporter molecule by use of microscopy, fluorimetry, a scintillation counter, or any available immunoassay. Binding can also be detected by labeling sclerostin in a competitive radioimmunoassay. Alternatively, sclerostin may be modified with an unlabeled epitope tag (e.g., biotin, peptides, His₆, FLAG, myc etc.) and bound to proteins such as streptavidin, anti-peptide or anti-protein antibodies that have a detectable label as described above. Additional forms of sclerostin containing epitope tags may be used in solution and immunoassays.

Methods for identifying compounds or molecules that interact with sclerostin are also encompassed by the invention. In general, an assay for identifying compounds or molecules that interact with sclerostin involves incubating sclerostin with a test sample that may contain such a compound or molecule under conditions that permit binding of the compound or molecule to sclerostin, and measuring whether binding has occurred. Sclerostin may be purified or present in mixtures, such as in cultured cells, tissue samples, body fluids or culture medium. Assays may be developed that are qualitative or quantitative. Quantitative assays can used for determining, the binding parameters (affinity constants and kinetics) of the compound or molecule for sclerostin and for quantifying levels of biologically active compounds and molecules in mixtures. Assays may also be used to evaluate the binding of a compound or molecule to fragments, analogs and derivatives of sclerostin and to identify new sclerostin family members.

The compound or molecule in a test sample may be substantially purified or present in a crude mixture. Binding compounds and molecules may be nucleic acids, proteins, peptides, carbohydrates, lipids or small molecular weight organic compounds. The compounds and molecules may be further characterized by their ability to increase or decrease sclerostin activity in order to determine whether they act as an agonist or an antagonist.

In another embodiment, the invention involves a method for identifying an agent that can modulate sclerostin-related apoptosis activity comprising contacting a cell with both sclerostin and a test agent and detecting whether the test sample prevents apoptosis of the cell. The amount of apoptosis in cells treated with sclerostin and a test agent can be compared to the amount of apoptosis in cells treated with sclerostin only. To detect the level of apoptosis, cell viability and apoptosis assays can be performed. Many cell viability assays are available to one of skill in the art and any of these can be used. For example, a CellTiterGlo Luminescence Viability Assay available from Promega can be used to assess cell viability. Apoptosis can be detected using any of the many available apoptosis assays. For example, the Homogeneous Caspase ELISA (Roche) or the Cell Death assay (Histone-Associated DNA Fragmentation, Roche) can be used. Apoptosis can also be detected by TUNEL staining using Roche's In Situ Cell Death Detection kit.

SOST nucleic acids are also useful for identification of factors that interact with the SOST promoter and that modulate SOST expression. Such factors may be intracellular proteins such as DNA binding proteins that interact with regulatory sequences that control SOST transcription, for example, the SOST promoter. As an example, hybrid constructs may be used that include a nucleic acid encoding the SOST promoter fused to a nucleic acid encoding a marker protein. The SOST promoter can be found within SEQ ID NO:1. The promoter used can, for example, have sequence SEQ ID NO:4.

The marker protein can be any marker protein available to one of skill in the art. For example, the marker protein can be luciferase, green fluorescence protein (GFP) or CAT.

Such constructs are used for in vitro or in vivo transcription assays to identify factors that modulate SOST expression. Factors that depress or diminish SOST expression are particularly useful. Expression or transcription levels can be assessed using any method available to one of skill in the art for measuring RNA levels. For example, RNA levels can be assessed by northern analysis, reverse transcriptase analysis, reverse transcriptase coupled with polymerase chain reaction (RT-PCR) analysis and other methods. Chemical libraries can be screened using such methods for small molecule compounds that block SOST transcription.

Sclerostin is involved in controlling formation of mature osteoblasts, the primary cell type implicated in bone mineralization. Factors that counteract the sclerostin-induced depression of mineralization can be identified by observing whether a test agent increases mineralization in cultured osteoblasts that have been exposed to sclerostin. Hence, an assay may involve contacting an osteoblast with sclerostin and a test agent and observing whether the mineralization of the cell is increased relative to a similar cell that is contacted only with sclerostin.

Many variations and modifications of the methods described herein will be apparent to one of skilled in the art. All such variations and modifications are encompassed by the invention.

Antibodies

The invention provides antibody preparations directed against sclerostin, for example, antibodies capable of binding a polypeptide having SEQ ID NO:3, SEQ ID NO:6 or SEQ ID NO:8.

Antibody molecules belong to a family of plasma proteins called immunoglobulins, whose basic building block, the immunoglobulin fold or domain, is used in various forms in many molecules of the immune system and other biological recognition systems. A typical immunoglobulin has four polypeptide chains, containing an antigen binding region known as a variable region and a non-varying region known as the constant region.

Native antibodies and immunoglobulins are usually heterotetrameric glycoproteins of about 150,000 daltons, composed of two identical light (L) chains and two identical heavy (H) chains. Each light chain is linked to a heavy chain by one covalent disulfide bond, while the number of disulfide linkages varies between the heavy chains of different immunoglobulin isotypes. Each heavy and light chain also has regularly spaced intrachain disulfide bridges. Each heavy chain has at one end a variable domain (VH) followed by a number of constant domains. Each light chain has a variable domain at one end (VL) and a constant domain at its other end. The constant domain of the light chain is aligned with the first constant domain of the heavy chain, and the light chain variable domain is aligned with the variable domain of the heavy chain. Particular amino acid residues are believed to form an interface between the light and heavy chain variable domains (Clothia et al., J. Mol. Biol. 186, 651-66, 1985); Novotny and Haber, Proc. Natl. Acad. Sci. USA 82, 4592-4596 (1985).

Depending on the amino acid sequences of the constant domain of their heavy chains, immunoglobulins can be assigned to different classes. There are at least five (5) major classes of immunoglobulins: IgA, IgD, IgE, IgG and IgM, and several of these may be further divided into subclasses (isotypes), e.g. IgG-1, IgG-2, IgG-3 and IgG-4; IgA-1 and IgA-2. The heavy chains constant domains that correspond to the different classes of immunoglobulins are called alpha (α), delta (δ), epsilon (ε), gamma (γ) and mu (μ), respectively. The light chains of antibodies can be assigned to one of two clearly distinct types, called kappa (κ) and lambda (λ), based on the amino sequences of their constant domain. The subunit structures and three-dimensional configurations of different classes of immunoglobulins are well known.

The term “variable” in the context of variable domain of antibodies, refers to the fact that certain portions of the variable domains differ extensively in sequence among antibodies. The variable domains are for binding and determine the specificity of each particular antibody for its particular antigen. However, the variability is not evenly distributed through the variable domains of antibodies. It is concentrated in three segments called complementarity determining regions (CDRs) also known as hypervariable regions both in the light chain and the heavy chain variable domains.

The more highly conserved portions of variable domains are called the framework (FR). The variable domains of native heavy and light chains each comprise four FR regions, largely adopting a β-sheet configuration, connected by three CDRs, which form loops connecting, and in some cases forming part of, the β-sleet structure. The CDRs in each chain are held together in close proximity by the FR regions and, with the CDRs from the other chain, contribute to the formation of the antigen-binding site of antibodies. The constant domains are not involved directly in binding an antibody to an antigen, but exhibit various effector functions, such as participation of the antibody in antibody-dependent cellular toxicity.

An antibody that is contemplated for use in the present invention thus can be in any of a variety of forms, including a whole immunoglobulin, an antibody fragment such as Fv, Fab, and similar fragments, a single chain antibody which includes the variable domain complementarity determining regions (CDR), and the like forms, all of which fall under the broad term “antibody”, as used herein. The present invention contemplates the use of any specificity of an antibody, polyclonal or monoclonal, and is not limited to antibodies that recognize and immunoreact with a specific antigen. In preferred embodiments, in the context of both the therapeutic and screening methods described below, an antibody or fragment thereof is used that is immunospecific for an antigen or epitope of the invention.

The term “antibody fragment” refers to a portion of a full-length) antibody, generally the antigen binding or variable region. Examples of antibody fragments include Fab, Fab′, F(ab′)₂ and Fv fragments. Papain digestion of antibodies produces two identical antigen binding fragments, called the Fab fragment, each with a single antigen binding site, and a residual “Fc” fragment, so-called for its ability to crystallize readily. Pepsin treatment yields an F(ab′)₂ fragment that has two antigen binding fragments that are capable of cross-linking antigen, and a residual other fragment (which is termed pFc′). Additional fragments can include diabodies, linear antibodies, single-chain antibody molecules, and multispecific antibodies formed from antibody fragments. As used herein, “functional fragment” with respect to antibodies, refers to Fv, F(ab) and F(ab′)₂ fragments.

Antibody fragments contemplated by the invention are therefore not full-length antibodies but do have similar or improved immunological properties relative to an anti-sclerostin antibody. Such antibody fragments may be as small as about 4 amino acids, 5 amino acids, 6 amino acids, 7 amino acids, 9 amino acids, about 12 amino acids, about 15 amino acids, about 17 amino acids, about 18 amino acids, about 20 amino acids, about 25 amino acids, about 30 amino acids or more. In general, an antibody fragment of the invention can have any upper size limit so long as it binds with specificity to sclerostin, e.g. a polypeptide having SEQ ID NO:3, 6 or 8.

Antibody fragments retain some ability to selectively bind with its antigen. Some types of antibody fragments are defined as follows:

(1) Fab is the fragment that contains a monovalent antigen-binding fragment of an antibody molecule. A Fab fragment can be produced by digestion of whole antibody with the enzyme papain to yield an intact light chain and a portion of one heavy chain.

(2) Fab′ is the fragment of an antibody molecule can be obtained by treating whole antibody with pepsin, followed by reduction, to yield an intact light chain) and a portion of the heavy chain. Two Fab′ fragments are obtained per antibody molecule. Fab′ fragments differ from Fab fragments by the addition of a few residues at the carboxyl terminus of the heavy chain CH1 domain including one or more cysteines from the antibody hinge region.

(3) (Fab′)₂ is the fragment of an antibody that can be obtained by treating whole antibody with the enzyme pepsin without subsequent reduction. F(ab′)₂ is a dimer of two Fab′ fragments held together by two disulfide bonds.

(4) Fv is the minimum antibody fragment that contains a complete antigen recognition and binding site. This region consists of a dimer of one heavy and one light chain variable domain in a tight non-covalent association (V_(H)-V_(L) dimer). It is in this configuration that the three CDRs of each variable domain interact to define an antigen binding site on the surface of the V_(H)-V_(L) diner. Collectively, the six CDRs confer antigen binding specificity to the antibody. However, even a single variable domain (or half of an Fv comprising only three CDRs specific for an antigen) has the ability to recognize and bind antigen, although at a lower affinity than the entire binding site.

(5) Single chain antibody (“SCA”), defined as a genetically engineered molecule containing the variable region of the light chain, the variable region of the heavy chain, linked by a suitable polypeptide linker as a genetically fused single chain molecule. Such single chain antibodies are also referred to as “single-chain Fv” or “sFv” antibody fragments. Generally, the Fv polypeptide further comprises a polypeptide linker between the VH and VL domains that enables the sFv to form the desired structure for antigen binding. For a review of sFv see Pluckthun in The Pharmacology of Monoclonal Antibodies, vol. 113, Rosenburg and Moore eds. Springer-Verlag, N.Y., pp. 269-315 (1994).

The term “diabodies” refers to a small antibody fragments with two antigen-binding sites, which fragments comprise a heavy chain variable domain (VH) connected to a light chain variable domain (VL) in the same polypeptide chain (VH-VL). By using a linker that is too short to allow pairing between the two domains on the same chain, the domains are forced to pair with the complementary domains of another chain and create two antigen-binding sites. Diabodies are described more fully in, for example, EP 404,097; WO 93/11161, and Hollinger et al., Proc. Natl. Acad. Sci. USA 90: 6444-6448 (1993).

Methods for preparing polyclonal antibodies are available to those skilled in the art. See, for example, Green, et al., Production of Polyclonal Antisera, in: Immunochemical Protocols (Manson, ed.), pages 1-5 (Humana Press); Coligan, et al., Production of Polyclonal Antisera in Rabbits, Rats Mice and Hamsters, in: Current Protocols in Immunology, section 2.4.1 (1992), which are hereby incorporated by reference.

Methods for preparing monoclonal antibodies are likewise available to one of skill in the art. See, for example, Kohler & Milstein, Nature, 256:495 (1975); Coligan, et al., sections 2.5.1-2.6.7; and Harlow, et al., in: Antibodies: A Laboratory Manual, page 726 (Cold Spring Harbor Pub. (1988)), which are hereby incorporated by reference. Monoclonal antibodies can be isolated and purified from hybridoma cultures by a variety of well-established techniques. Such isolation techniques include affinity chromatography with Protein-A Sepharose, size-exclusion chromatography, and ion-exchange chromatography. See, e.g., Coligan, et al., sections 2.7.1-2.7.12 and sections 2.9.1-2.9.3; Barnes, et al., Purification of Immunoglobulin G (IgG), in: Methods in Molecular Biology, Vol. 10, pages 79-104 (Humana Press (1992).

Methods of in vitro and in vivo manipulation of monoclonal antibodies are also available to those skilled in the art. For example, monoclonal antibodies to be used in accordance with the present invention may be made by the hybridoma method first described by Kohler and Milstein, Nature 256, 495 (1975), or may be made by recombinant methods, e.g., as described in U.S. Pat. No. 4,816,567. The monoclonal antibodies for use with the present invention may also be isolated from phage antibody libraries using the techniques described in Clackson et al. Nature 352: 624-628 (1991), as well as in Marks et al., J. Mol. Biol. 222: 581-597 (1991). Another method involves humanizing a monoclonal antibody by recombinant means to generate antibodies containing human specific and recognizable sequences. See, for review, Holmes, et al., J. Immunol., 158:2192-2201 (1997) and Vaswani, et al., Annals Allergy, Asthma & Immunol., 81:105-115 (1998).

The term “monoclonal antibody” as used herein refers to an antibody obtained from a population of substantially homogeneous antibodies, i.e., the individual antibodies comprising the population are identical except for possible naturally occurring mutations that may be present in minor amounts. Monoclonal antibodies are highly specific, being directed against a single antigenic site. Furthermore, in contrast to conventional polyclonal antibody preparations that typically include different antibodies directed against different determinants (epitopes), each monoclonal antibody is directed against a single determinant on the antigen. In additional to their specificity, the monoclonal antibodies are advantageous in that they are synthesized by the hybridoma culture, uncontaminated by other immunoglobulins. The modifier “monoclonal” indicates that the antibody preparation is a substantially homogeneous population of antibodies, and is not to be construed as requiring production of the antibody by any particular method.

The monoclonal antibodies herein specifically include “chimeric” antibodies (immunoglobulins) in which a portion of the heavy and/or light chain is identical with or homologous to corresponding sequences in antibodies derived from a particular species or belonging to a particular antibody class or subclass, while the remainder of the chain(s) is identical with or homologous to corresponding sequences in antibodies derived from another species or belonging to another antibody class or subclass, as well as fragments of such antibodies, so long as they exhibit the desired biological activity (U.S. Pat. No. 4,816,567); Morrison et al., Proc. Nat). Acad. Sci. 81, 6851-6855 (1984).

Methods of making antibody fragments are also known in the art (see for example, Harlow and Lane, Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, New York, (1988), incorporated herein by reference). Antibody fragments of the present invention can be prepared by proteolytic hydrolysis of the antibody or by expression in E. coli of DNA encoding the fragment. Antibody fragments can be obtained by pepsin or papain digestion of whole antibodies conventional methods. For example, antibody fragments can be produced by enzymatic cleavage of antibodies with pepsin to provide a 5S fragment denoted F(ab′)₂. This fragment can be further cleaved using a thiol reducing agent, and optionally a blocking group for the sulfhydryl groups resulting from cleavage of disulfide linkages, to produce 3.5S Fab′ monovalent fragments. Alternatively, an enzymatic cleavage using pepsin produces two monovalent Fab′ fragments and an Fc fragment directly. These methods are described, for example, in U.S. Pat. No. 4,036,945 and No. 4,331,647, and references contained therein. These patents are hereby incorporated in their entireties by reference.

Other methods of cleaving antibodies, such as separation of heavy chains to form monovalent light-heavy chain fragments, further cleavage of fragments, or other enzymatic, chemical, or genetic techniques may also be used, so long as the fragments bind to the antigen that is recognized by the intact antibody. For example, Fv fragments comprise an association of V_(H) and V_(L) chains. This association may be non-covalent or the variable chains can be linked by an intermolecular disulfide bond or cross-linked by chemicals such as glutaraldehyde. Preferably, the Fv fragments comprise V_(H) and V_(L) chains connected by a peptide linker. These single-chain antigen binding proteins (sFv) are prepared by constructing a structural gene comprising DNA sequences encoding the V_(H) and V_(L) domains connected by an oligonucleotide. The structural gene is inserted into an expression vector, which is subsequently introduced into a host cell such as E. coli. The recombinant host cells synthesize a single polypeptide chain with a linker peptide bridging the two V domains. Methods for producing sFvs are described, for example, by Whitlow, et al., Methods: a Companion to Methods in Enzymology, Vol. 2, page 97 (1991); Bird, et al., Science 242:423-426 (1988); Ladner, et al, U.S. Pat. No. 4,946,778; and Pack, et al., Bio/Technology 11:1271-77 (1993).

Another form of an antibody fragment is a peptide coding for a single complementarity-determining region (CDR). CDR peptides (“minimal recognition units”) are often involved in antigen recognition and binding. CDR peptides can be obtained by cloning or constructing genes encoding the CDR of an antibody of interest. Such genes are prepared, for example, by using the polymerase chain reaction to synthesize the variable region from RNA of antibody-producing cells. See, for example, Larrick, et al., Methods: a Companion to Methods in Enzymology, Vol. 2, page 106 (1991).

The invention contemplates human and humanized forms of non-human (e.g. murine) antibodies. Such humanized antibodies are chimeric immunoglobulins, immunoglobulin chains or fragments thereof (such as Fv, Fab, Fab′, F(ab′)₂ or other antigen-binding subsequences of antibodies) that contain minimal sequence derived from nonhuman immunoglobulin. For the most part, humanized antibodies are human immunoglobulins (recipient antibody) in which residues from a complementary determining region (CDR) of the recipient are replaced by residues from a CDR of a nonhuman species (donor antibody) such as mouse, rat or rabbit having the desired specificity, affinity and capacity.

In some instances, Fv framework residues of the human immunoglobulin are replaced by corresponding non-human residues. Furthermore, humanized antibodies may comprise residues that are found neither in the recipient antibody nor in the imported CDR or framework sequences. These modifications are made to further refine and optimize antibody performance. In general, humanized antibodies will comprise substantially all of at least one, and typically two, variable domains, in which all or substantially all of the CDR regions correspond to those of a non-human immunoglobulin and all or substantially all of the FR regions are those of a human immunoglobulin consensus sequence. The humanized antibody optimally also will comprise at least a portion of an immunoglobulin constant region (Fc), typically that of a human immunoglobulin. For further details, see: Jones et al., Nature 321, 522-525 (1986); Reichmann et al., Nature 332, 323-329 (1988); Presta, Curr. Op. Struct. Biol. 2, 593-596 (1992); Holmes, et al., J. Immunol., 158:2192-2201 (1997) and Vaswani, et al., Animals Allergy, Asthma & Immunol., 81:105-115 (1998).

The invention also provides methods of mutating antibodies to optimize their affinity, selectivity, binding strength or other desirable property. A mutant antibody refers to an amino acid sequence variant of an antibody. In general, one or more of the amino acid residues in the mutant antibody is different from what is present in the reference antibody. Such mutant antibodies necessarily have less than 100% sequence identity or similarity with the reference amino acid sequence. In general, mutant antibodies have at least 75% amino acid sequence identity or similarity with the amino acid sequence of either the heavy or light chain variable domain of the reference antibody. Preferably, mutant antibodies have at least 80%, more preferably at least 85%, even more preferably at least 90%, and most preferably at least 95% amino acid sequence identity or similarity with the amino acid sequence of either the heavy or light chain variable domain of the reference antibody. One method of mutating antibodies involves affinity maturation using phage display.

The invention is therefore directed to a method for selecting antibodies and/or antibody fragments or antibody polypeptides with desirable properties. Such desirable properties can include increased binding affinity or selectivity for the epitopes of the invention

The antibodies and antibody fragments of the invention are isolated antibodies and antibody fragments. An isolated antibody is one that has been identified and separated and/or recovered from a component of the environment in which it was produced. Contaminant components of its production environment are materials that would interfere with diagnostic or therapeutic uses for the antibody, and may include enzymes, hormones, and other proteinaceous or nonproteinaceous solutes. The term “isolated antibody” also includes antibodies within recombinant cells because at least one component of the antibody's natural environment will not be present. Ordinarily, however, isolated antibody will be prepared by at least one purification step

If desired, the antibodies of the invention can be purified by any available procedure. For example, the antibodies can be affinity purified by binding an antibody preparation to a solid support to which the antigen used to raise the antibodies is bound. After washing off contaminants, the antibody can be eluted by known procedures. Those of skill in the art will know of various techniques common in the immunology arts for purification and/or concentration of polyclonal antibodies, as well as monoclonal antibodies (see for example, Coligan, et al., Unit 9, Current Protocols in Immunology, Wiley Interscience, 1991, incorporated by reference).

In preferred embodiments, the antibody will be purified as measurable by at least three different methods: 1) to greater than 95% by weight of antibody as determined by the Lowry method, and most preferably more than 99% by weight; 2) to a degree sufficient to obtain at least 15 residues of N-terminal or internal amino acid sequence by use of a spinning cup sequentator; or 3) to homogeneity by SDS-PAGE under reducing or non-reducing conditions using Coomasie blue or, preferably, silver stain.

Compositions

The sclerostin antagonists and other agents (e.g. sclerostin proteins and SOST nucleic acids) of the invention, including their salts, are administered so as to achieve a reduction in at least one symptom associated with a bone disorder, indication or disease.

To achieve the desired effect(s), sclerostin antagonists and other agents, may be administered as single or divided dosages, for example, of at least about 0.01 mg/kg to about 500 to 750 mg/kg, of at least about 0.01 mg/kg to about 300 to 500 mg/kg, at least about 0.1 mg/kg to about 100 to 300 mg/kg or at least about 1 mg/kg to about 50 to 100 mg/kg of body weight, although other dosages may provide beneficial results. The amount administered will vary depending on various factors including, but not limited to, the sclerostin antagonist or other agent chosen, the disease, the weight, the physical condition, the health, the age of the mammal, whether prevention or treatment is to be achieved, and if the sclerostin antagonist or agent is chemically modified. Such factors can be readily determined by the clinician employing animal models or other test systems that are available in the art.

Administration of the therapeutic agents in accordance with the present invention may be in a single dose, in multiple doses, in a continuous or intermittent manner, depending, for example, upon the recipient's physiological condition, whether the purpose of the administration is therapeutic or prophylactic, and other factors known to skilled practitioners. The administration of the therapeutic agents of the invention may be essentially continuous over a preselected period of time or may be in a series of spaced doses. Both local and systemic administration is contemplated.

To prepare the composition, therapeutic agents are synthesized or otherwise obtained, purified as necessary or desired and then lyophilized and stabilized. The therapeutic agent can then be adjusted to the appropriate concentration, and optionally combined with other agents. The absolute weight of a given therapeutic agent included in a unit dose can vary widely. For example, about 0.01 to about 2 g, or about 0.1 to about 500 mg, of at least one therapeutic agents of the invention, or a plurality of therapeutic agents can be administered. Alternatively, the unit dosage can vary from about 0.01 g to about 50 g, from about 0.01 g to about 35 g, from about 0.1 g to about 25 g, from about 0.5 g to about 12 g, from about 0.5 g to about 8 g, from about 0.5 g to about 4 g, or from about 0.5 g to about 2 g.

Daily doses of the therapeutic agents of the invention can vary as well, Such daily doses can range, for example, from about 0.1 g/day to about 50 g/day, from about 0.1 g/day to about 25 g/day, from about 0.1 g/day to about 12 g/day, from about 0.5 g/day to about 8 g/day, from about 0.5 g/day to about 4 g/day, and from about 0.5 g/day to about 2 g/day.

Thus, one or more suitable unit dosage forms comprising the therapeutic agents of the invention can be administered by a variety of routes including oral, parenteral (including subcutaneous, intravenous, intramuscular and intraperitoneal), rectal, dermal, transdermal, intrathoracic, intrapulmonary and intranasal (respiratory) routes. The therapeutic agents may also be formulated for sustained release (for example, using microencapsulation, see WO 94/07529, and U.S. Pat. No. 4,962,091). The formulations may, where appropriate, be conveniently presented in discrete unit dosage forms and may be prepared by any of the methods well known to the pharmaceutical arts. Such methods may include the step of mixing the therapeutic agent with liquid carriers, solid matrices, semi-solid carriers, finely divided solid carriers or combinations thereof, and then, if necessary, introducing or shaping the product into the desired delivery system.

When the therapeutic agents of the invention are prepared for oral administration, they are generally combined with a pharmaceutically acceptable carrier, diluent or excipient to form a pharmaceutical formulation, or unit dosage form. For oral administration, the therapeutic agents may be present as a powder, a granular formulation, a solution, a suspension, an emulsion or in a natural or synthetic polymer or resin for ingestion of the active ingredients from a chewing gum. The therapeutic agents may also be presented as a bolus, electuary or paste. Orally administered therapeutic agents of the invention can also be formulated for sustained release, e.g., the therapeutic agents can be coated, micro-encapsulated, or otherwise placed within a sustained delivery device. The total active ingredients in such formulations comprise from 0.1 to 99.9% by weight of the formulation.

By “pharmaceutically acceptable” it is meant a carrier, diluent, excipient, and/or salt that is compatible with the other ingredients of the formulation, and not deleterious to the recipient thereof.

Pharmaceutical formulations containing the therapeutic agents of the invention can be prepared by procedures known in the art using well-known and readily available ingredients. For example, the therapeutic agent can be formulated with common excipients, diluents, or carriers, and formed into tablets, capsules, solutions, suspensions, powders, aerosols and the like. Examples of excipients, diluents, and carriers that are suitable for such formulations include buffers, as well as fillers and extenders such as starch, cellulose, sugars, mannitol, and silicic derivatives. Binding agents can also be included such as carboxylmethyl cellulose, hydroxymethylcellulose, hydroxypropyl methylcellulose and other cellulose derivatives, alginates, gelatin, and polyvinyl-pyrrolidone. Moisturizing agents can be included such as glycerol, disintegrating agents such as calcium carbonate and sodium bicarbonate. Agents for retarding dissolution can also be included such as paraffin. Resorption accelerators such as quaternary ammonium compounds can also be included. Surface-active agents such as cetyl alcohol and glycerol monostearate can be included. Adsorptive carriers such as kaolin and bentonite can be added. Lubricants such as talc, calcium and magnesium stearate, and solid polyethyl glycols can also be included. Preservatives may also be added. The compositions of the invention can also contain thickening agents such as cellulose and/or cellulose derivatives. They may also contain gums such as xanthan, guar or carbo gum or gum arabic, or alternatively polyethylene glycols, bentones and montmorillonites, and the like.

For example, tablets or caplets containing the therapeutic agents of the invention can include buffering agents such as calcium carbonate, magnesium oxide and magnesium carbonate. Caplets and tablets can also include inactive ingredients such as cellulose, pre-gelatinized starch, silicon dioxide, hydroxy propyl methyl cellulose, magnesium stearate, microcrystalline cellulose, starch, talc, titanium dioxide, benzoic acid, citric acid, corn starch, mineral oil, polypropylene glycol, sodium phosphate, zinc stearate, and the like. Hard or soft gelatin capsules containing: at least one therapeutic agent of the invention can contain inactive ingredients such as gelatin, microcrystalline cellulose, sodium lauryl sulfate, starch, talc, and titanium dioxide, and the like, as well as liquid vehicles such as polyethylene glycols (PEGs) and vegetable oil. Moreover, enteric-coated caplets or tablets containing one or more therapeutic agent of the invention are designed to resist disintegration in the stomach and dissolve in the more neutral to alkaline environment of the duodenum.

The therapeutic agents of the invention can also be formulated as elixirs or solutions for convenient oral administration or as solutions appropriate for parenteral administration, for instance by intramuscular, subcutaneous, intraperitoneal or intravenous routes. The pharmaceutical formulations of the therapeutic agents of the invention can also take the form of an aqueous or anhydrous solution or dispersion, or alternatively the form of an emulsion or suspension or salve.

Thus, the therapeutic agents may be formulated for parenteral administration (e.g., by injection, for example, bolus injection or continuous infusion) and may be presented in unit dose form in ampoules, pre-filled syringes, small volume infusion containers or in multi-dose containers. As noted above, preservatives can be added to help maintain the shelve life of the dosage form. The therapeutic agents and other ingredients may form suspensions, solutions, or emulsions in oily or aqueous vehicles, and may contain formulatory agents such as suspending, stabilizing and/or dispersing agents. Alternatively, the therapeutic agents and other ingredients may be in powder form, obtained by aseptic isolation of sterile solid or by lyophilization from solution, for constitution with a suitable vehicle, e.g., sterile, pyrogen-free water, before use.

These formulations can contain pharmaceutically acceptable carriers, vehicles and adjuvants that are well known in the art. It is possible, for example, to prepare solutions using one or more organic solvent(s) that is/are acceptable from the physiological standpoint, chosen, in addition to water, from solvents such as acetone, ethanol, isopropyl alcohol, glycol ethers such as the products sold under the name “Dowanol,” polyglycols and polyethylene glycols, C₁-C₄ alkyl esters of short-chain acids, ethyl or isopropyl lactate, fatty acid triglycerides such as the products marketed under the name “Miglyol,” isopropyl myristate, animal, mineral and vegetable oils and polysiloxanes.

It is possible to add, if necessary, an adjuvant chosen from antioxidants, surfactants, other preservatives, film-forming, keratolytic or comedolytic agents, perfumes, flavorings and colorings. Antioxidants such as t-butylhydroquinone, butylated hydroxyanisole, butylated hydroxytoluene and α-tocopherol and its derivatives can be added.

Also contemplated are combination products that include one or more of the therapeutic agents of the present invention and one or more other ingredients. For example, the compositions can contain vitamins, minerals (e.g. calcium), anti-inflammatory agents and the like.

Additionally, the therapeutic agents are well suited to formulation as sustained release dosage forms and the like. The formulations can be so constituted that they release the therapeutic agents, for example, in a particular part of the intestinal or respiratory tract, possibly over a period of time. Coatings, envelopes, and protective matrices may be made, for example, from polymeric substances, such as polylactide-glycolates, liposomes, microemulsions, microparticles, nanoparticles, or waxes. These coatings, envelopes, and protective matrices are useful to coat indwelling devices, e.g., tissue re-modeling devices, pins, splints, joint replacement devices and the like.

For topical administration, the therapeutic agents may be formulated as is known in the art for direct application to a target area. Forms chiefly conditioned for topical application take the form, for example, of creams, milks, gels, dispersion or microemulsions, lotions thickened to a greater or lesser extent, impregnated pads, ointments or sticks, aerosol formulations (e.g., sprays or foams), soaps, detergents, lotions or cakes of soap. Other conventional forms for this purpose include wound dressings, coated bandages or other polymer coverings, ointments, creams, lotions, pastes, jellies, sprays, and aerosols. Thus, the therapeutic agents of the invention can be delivered via patches or bandages for dermal administration. Alternatively, the therapeutic agent can be formulated to be part of an adhesive polymer, such as polyacrylate or acrylate/vinyl acetate copolymer. For long-term applications it might be desirable to use microporous and/or breathable backing laminates, so hydration or maceration of the skin can be minimized. The backing layer can be any appropriate thickness that will provide the desired protective and support functions. A suitable thickness will generally be from about 10 to about 200 microns.

Ointments and creams may, for example, be formulated with an aqueous or oily base with the addition of suitable thickening and/or gelling agents. Lotions may be formulated with an aqueous or oily base and will in general also contain one or more emulsifying agents, stabilizing agents, dispersing agents, suspending agents, thickening agents, or coloring agents. The therapeutic agents can also be delivered via iontophoresis, e.g., as disclosed in U.S. Pat. Nos. 4,140,122; 4,383,529; or 4,051,842. The percent by weight of a therapeutic agent of the invention present in a topical formulation will depend on various factors, but generally will be from 0.01% to 95% of the total weight of the formulation, and typically 0.1-85% by weight.

Drops, such as eye drops or nose drops, may be formulated with one or more of the therapeutic agents in an aqueous or non-aqueous base also comprising one or more dispersing agents, solubilizing agents or suspending agents. Liquid sprays are conveniently delivered from pressurized packs. Drops can be delivered via a simple eye dropper-capped bottle, or via a plastic bottle adapted to deliver liquid contents dropwise, via a specially shaped closure.

The therapeutic agents may further be formulated for topical administration in the mouth or throat. For example, the active ingredients may be formulated as a lozenge further comprising a flavored base, usually sucrose and acacia or tragacanth; pastilles comprising the composition in an inert base such as gelatin and glycerin or sucrose and acacia.

The pharmaceutical formulations of the present invention may include, as optional ingredients, pharmaceutically acceptable carriers, diluents, solubilizing or emulsifying agents, and salts of the type that are available in the art. Examples of such substances include normal saline solutions such as physiologically buffered saline solutions and water. Specific non-limiting examples of the carriers and/or diluents that are useful in the pharmaceutical formulations of the present invention include water and physiologically acceptable buffered saline solutions such as phosphate buffered saline solutions pH 7.0-8.0.

The therapeutic agents of the invention can also be administered to the respiratory tract. Thus, the present invention also provides aerosol pharmaceutical formulations and dosage forms for use in the methods of the invention. In general, such dosage forms comprise an amount of at least one of the agents of the invention effective to treat or prevent the clinical symptoms of a specific bone disorder or disease. Any statistically significant attenuation of one or more symptoms of the disorder or disease that has been treated pursuant to the method of the present invention is considered to be a treatment of such disorder or disease within the scope of the invention.

Alternatively, for administration by inhalation or insufflation, the composition may take the form of a dry powder, for example, a powder mix of the therapeutic agent and a suitable powder base such as lactose or starch. The powder composition may be presented in unit dosage form in, for example, capsules or cartridges, or, e.g., gelatin or blister packs from which the powder may be administered with the aid of an inhalator, insufflator, or a metered-dose inhaler (see, for example, the pressurized metered dose inhaler (MDI) and the dry powder inhaler disclosed in Newman, S. P. in Aerosols and the Lung, Clarke, S. W. and Davia, D. eds., pp. 197-224, Butterworths, London, England, 1984).

Therapeutic agents of the present invention can also be administered in an aqueous solution when administered in an aerosol or inhaled form. Thus, other aerosol pharmaceutical formulations may comprise, for example, a physiologically acceptable buffered saline solution containing between about 0.1 mg/ml and about 100 mg/ml of one or more of the therapeutic agents of the present invention specific for the indication or disease to be treated. Dry aerosol in the form of finely divided solid particles that are not dissolved or suspended in a liquid are also useful in the practice of the present invention. Therapeutic agents of the present invention may be formulated as dusting powders and comprise finely divided particles having an average particle size of between about 1 and 5 μm, alternatively between 2 and 3 μm. Finely divided particles may be prepared by pulverization and screen filtration using techniques well known in the art. The particles may be administered by inhaling a predetermined quantity of the finely divided material, which can be in the form of a powder. It will be appreciated that the unit content of active ingredient or ingredients contained in an individual aerosol dose of each dosage form need not in itself constitute an effective amount for treating the particular indication or disease since the necessary effective amount can be reached by administration of a plurality of dosage units. Moreover, the effective amount may be achieved using less than the dose in the dosage form, either individually, or in a series of administrations.

For administration to the upper (nasal) or lower respiratory tract by inhalation, the therapeutic agents of the invention are conveniently delivered from a nebulizer or a pressurized pack or other convenient means of delivering an aerosol spray. Pressurized packs may comprise a suitable propellant such as dichlorodifluoromethane, trichlorofluoromethane, dichlorotetrafluoroethane, carbon dioxide or other suitable gas. In the case of a pressurized aerosol, the dosage unit may be determined by providing a valve to deliver a metered amount. Nebulizers include, but are not limited to, those described in U.S. Pat. Nos. 4,624,251; 3,703,173; 3,563,444; and 4,635,627. Aerosol delivery systems of the type disclosed herein are available from numerous commercial sources including Fisons Corporation (Bedford, Mass.), Schering Corp. (Kenilworth, N.J.) and American Pharmoseal Co., (Valencia, Calif.). For intra-nasal administration, the therapeutic agent may also be administered via nose drops, a liquid spray, such as via a plastic bottle atomizer or metered-dose inhaler. Typical of atomizers are the Mistometer (Wintrop) and the Medihaler (Riker).

Furthermore, the active ingredients may also be used in combination with other therapeutic agents, for example, pain relievers, anti-inflammatory agents, vitamins, minerals and the like, whether for the conditions described or some other condition.

The present invention further pertains to a packaged pharmaceutical composition for controlling bone disorders such as a kit or other container. The kit or container holds a therapeutically effective amount of a pharmaceutical composition for controlling bone disorders and instructions for using the pharmaceutical composition for control of the bone disorder. The pharmaceutical composition includes at least one therapeutic agent of the present invention, in a therapeutically effective amount such that bone disorder is controlled.

All references cited herein are incorporated by reference in their entirety. The following examples illustrate certain aspects of the invention and are not intended to limit the scope thereof.

EXAMPLES

The following materials were used in these examples.

Primary human mesenchymal cells, primary human osteoblasts and corresponding media were purchased from Biowhittaker (Walkersville, Md.). Mouse mesenchymal C3H10T1/2 cells were obtained from American Type Culture Collection (Manassas, Va.) (ATCC Deposit No. CCL-226). Total RNA prepared from abdominal adipose tissue was obtained from Biochain Institute (Hayward, Calif.). General tissue culture reagents, first strand cDNA synthesis kits and Platinum Taq DNA polymerase were purchased from Invitrogen (Rockville, Md.). Noggin, gremlin, chordin, twisted gastrulation, and bone morphogenetic proteins 2, 4 and 6 were purchased from R & D Systems (Minneapolis, Minn.). Strataprep Total RNA mini-prep kits were purchased from Stratagene (San Diego, Calif.). Sephadex G-25 pre-packed NAP-5 columns were purchased from Amersham Biosciences (Piscataway, N.J.). Reagents for determining alkaline phosphatase (ALP) activity were obtained from Pierce-Endogen (Rockford, Ill.). Prolagen C ELISA kits were purchased from Quidel Corporation (Mountainview, Calif.). CellTiterGlo Cell Viability kits were obtained from Promega (Madison, Wis.). Homogeneous Caspase ELISA, Cell Death assay (Histone-Associated DNA Fragmentation), and In Situ Cell Death Detection kits were purchased from Roche Diagnostics (Indianapolis, Ind.). Caspase inhibitors (Caspase-1, Inhibitor VI and Caspase-3, Inhibitor 1) were obtained from Calbiochem (San Diego, Calif.). All other reagents and chemicals were purchased from Sigma (St. Louis, Mo.).

Example 1 Expression of SOST Correlates with Commitment and Differentiation of Precursor Cells to Osteogenic Lineage

In this example, the SOST expression was correlated with cellular differentiation and was found to increase as progenitor cells developed into osteoblasts.

SOST Expression Assay

Human mesenchymal (hMSC) cells were cultured in regular growth media (Biowhittaker's MSCGM) or Osteoblast-inducing media (Biowhittaker's MSCGM medium supplemented with 100 nM dexamethasone, 50 μg/ml ascorbic acid, and 10 mM β-glycerophosphate). Media were refreshed twice per week. Cultures were harvested 1, 7 and 21 days after plating and RNA isolated for RT-PCR analyses of SOST. SOST expression was also determined in adipocytes and chondrocytes generated from mesenchymal cells cultured for 21 to 28 days in corresponding media (Pittenger et al.). Primary cultures of human osteoblasts were also grown in Osteoblast-inducing media for 21 days and RNA isolated for RT-PCR. SOST expression was also analyzed in preparations of total RNA isolated from abdominal adipose tissue and from cartilagenous ends of long bones.

Results

Cell culture conditions necessary for human-derived mesenchymal (hMSC) cells to differentiate into osteoblast-like cells were developed. Mesenchymal cells are a population of bone marrow-derived pluripotent cells capable of differentiating into a number of different tissue types including bone, cartilage, fat, smooth muscle, tendon, marrow stroma, and neurons (Owen, 1998).

FIG. 1 a provides an RT-PCR analyses of RNA prepared from primary human osteoblasts, undifferentiated hMSC cells and hMSC cells differentiated to yield osteoblastic, chondrocytic and adipocytic cells. The expression of characteristic phenotypic markers (e.g. PPARγ2 for adipocytes) in these cell types was compared with that of SOST. As can be observed in FIG. 1 a, undifferentiated hMSC cells and adipocytes expressed negligible levels of SOST. In contrast, the cell types capable of mineralization that express markers associated with the osteoblast phenotype (typed I collagen, type X collagen, parathyroid hormone receptor (PTHr)) expressed SOST. These included cultures of primary human osteoblasts, hMSC cells differentiated to yield osteoblastic cells and hypertrophic chondrocytes.

The expression of the SOST in hMSC cells that had differentiated into osteoblast-like cells was correlated with the stage of osteoblast differentiation by observing hMSC cells grown in osteoblast-inducing medium over a 21-day period. hMSC cells differentiated into osteoblasts as indicated by enhanced histochemical staining for ALP and collagen (FIG. 1 b, darker stains in right panel at 21 days respectively) and deposition of mineral (negligible at Day 7 versus 437±60 μg calcium/mg protein at Day 28). Undifferentiated hMSC cells expressed negligible levels of SOST mRNA as well as negligible levels of mRNA correlating with alkaline phosphatase (ALP) activity, collagen and mineral deposition (FIG. 1 b, left panel). In contrast, the expression of ALP, collagen and SOST increased with time in cells grown in osteoblast-inducing media.

These results indicate that SOST expression increases in cells committed to osteoblast differentiation.

Example 2 Regulation of SOST Expression by Growth Factors and Hormones in Human Bone Cells

In this example, the effect of growth factors and hormones on SOST expression in hMSC cells or primary human osteoblasts was observed using RT-PCR. Prior to measuring SOST expression, these cells were treated for 72 hrs with BMP-2, BMP-4, BMP-6, insulin-like growth factor-1 (IGF-1), parathyroid hormone (PTH), transforming growth factor-β (TGF-β), dexamethasone (DEX), retinoic acid (RA), and 1,25-dihydroxyvitamin D₃ (vit D). As immature osteoblasts differentiate and become capable of mineralization, they express markers associated with the osteoblast phenotype (type I collagen and parathyroid hormone receptor (PTHr)). These markers were used to ascertain whether differentiation had occurred so that the influence of growth factors and hormones could be correlated with the stage differentiation as well as the level of SOST expression.

Methods

Human mesenchymal cells and primary human osteoblasts were plated in regular growth media containing 2% FCS at a density of 10,000 cells 1 cm². Test reagents (10⁻⁷ M dexamethasone, 10⁻⁶ M retinoic acid, 10 ng/ml TGF-β1, PTH (10⁻⁸ M), 10 or 50 ng/ml IGF-1, 10⁻⁷ M1,25-dihydroxyvitamin D₃, and 50 to 300 ng/ml of bone morphogenetic proteins 2, 4 or 6) were added singly or in combination on the following day. Cultures were continued for 24 to 120 hrs after which the cells were harvested for RNA isolation.

Results

FIGS. 2 to 6 show the results of these experiments. As can be seen in FIG. 2, while untreated hMSC cells (“vehicle”) strongly expressed type I collagen, they had negligible levels of PTHr and SOST (Vehicle and Control, 21 days). These results indicate that untreated hMSC cells are in an early stage of osteoblast lineage, but are committed to osteoblastogenesis. Treatment of these cells with dexamethasone, bone morphogenetic proteins, IGF-1 (IGF-1 at 50 ng/ml) or long-term culture in osteoblast-inducing media (Induced, 21 days) advanced the stage of differentiation and induced PTHr expression.

Several factors also enhanced the expression of SOST, including BMP-4, BMP-6, and IGF-1. Interestingly, factors such as vitamin D, PTH, TGF-β and dexamethasome by themselves had no effect on SOST expression. Bone morphogenetic proteins enhanced the expression of SOST in differentiating hMSC cells and in primary cultures of human osteoblasts.

FIG. 3 provides a time course of BMP-induced expression of SOST in hMSC and primary human osteoblasts. As shown, maximum levels of SOST expression were achieved within 72 to 120 hrs after start of treatment (FIG. 3).

The proteins noggin and gremlin are thought to function as BMP antagonists by binding and inactivating bone morphogenetic proteins (Yamaguchi et al. 2000). Bone morphogenetic proteins are also thought to regulate the expressions of noggin and gremlin in osteoblastic cells in culture. See Gazzero et al. (1998); Pereira et al (2000); and Nifuji & Noda (1999). The effect of bone morphogenetic proteins on SOST expression was compared to the effect of bone morphogenetic proteins on noggin and gremlin expression.

FIG. 4 shows that while the basal levels of SOST and noggin were negligible in undifferentiated hMSC cells, the levels of these genes were up-regulated by BMPs-2, 4 and 6. In contrast, gremlin was constitutively expressed in undifferentiated hMSC cells and its expression was only modestly increased by the bone morphogenetic proteins.

Steroids such as retinoids have been shown to regulate the differentiation of mesenchymal and osteoblastic cells (Gazit et al, 1999; Weston et al., 2000). The cellular response to steroids is modulated through interplay between the steroid hormone and TGF-β signaling pathways (Yanagi et al., 1999).

To determine whether steroids and/or the TGF-β signaling pathway affect BMP-mediated regulation of SOST expression, hMSC and osteoblastic cells were incubated with vitamin D, retinoic acid, and dexamethasone alone or in combination with BMP-4 for 72 hrs prior to RT-PCR analyses of SOST expression.

As shown in FIG. 5, steroids alone (vitamin D, retinoic acid, and dexamethasone) had no effect on the basal expression of SOST in hMSC or osteoblastic cells. However, BMP-4 enhanced SOST expression (FIG. 5). Interestingly, retinoic acid and vitamin D enhanced the levels of SOST when added in combination with BMP-4 such that the levels detected were greater than) those found in cells treated with BMP-4 alone.

In contrast, there was a decrease in SOST expression levels when dexamethasone was added with BMP-4. Therefore, dexamethasone apparently abolished the stimulatory effect of BMP on SOST expression (FIG. 5).

BMP-4 also enhanced gremlin and noggin expression (FIG. 6). However, steroids affected BMP-4 induced expression of gremlin and noggin somewhat differently than BMP-4 induced expression of SOST (FIG. 6). Like SOST, gremlin expression was unchanged in cells treated only with retinoic acid or vitamin D. Unlike SOST, basal levels of gremlin decreased when cells were treated with dexamethasone alone. But the stimulatory effect of BMP-4 on gremlin expression was diminished when retinoic acid and dexamethasone were added with BMP-4. Vitamin D did not alter the effect of BMP-4 on gremlin expression.

In contrast, BMP-4, retinoic acid, dexamethasone and vitamin D all appeared to increase the levels of noggin in hMSC cells. BMP-4 exerted the greatest effect. The stimulatory effect of BMP-4 on noggin was not greatly altered by steroids.

Therefore, the effects of steroids and BMP-4 on gremlin and noggin contrasted markedly with those on SOST (FIG. 6). BMP-4 significantly increased the levels of SOST expression and this effect was enhanced in the presence of vitamin D or retinoic acid but not with dexamethasone. In fact, dexamethasone significantly suppressed SOST expression.

Example 3 Compounds Affecting SOST Expression

The previous example illustrates that SOST expression was enhanced by bone morphogenetic proteins and modulated by steroids such as dexamethasone. In this example, human MSC cells were incubated with bone morphogenetic proteins in the presence of various test agents to determine whether other steroids and compounds could affect the BMP-induction of SOST. SOST expression was monitored by reverse transcriptase polymerase chain reaction (RT-PCR).

Materials and Methods

Human mesenchymal cells (hMSCs) were plated in regular growth media containing 2% FCS and treated with BMP-6 either alone or in combination with the test compounds. The cells were harvested 72 hrs later and RNA was prepared for RT-PCR analysis of SOST expression.

Results

The compounds tested and the results obtained for these compounds are summarized in Table 1.

TABLE 1 Compound Concentration Compound Source Type Tested Results Dexamethasone SIGMA- Glucocorticoid 1 × 10⁻⁷ M Inhibition Aldrich analog Triamcinolone SIGMA- Glucocorticoid 1 × 10⁻⁷ M Inhibition Aldrich analog Fluocinolone acetonide SIGMA- Glucocorticoid 1 × 10⁻⁷ M Inhibition Aldrich analog Ursodeoxycholic acid SIGMA- Bile salt 1 × 10⁻⁶ M Inhibition Aldrich 3 × 10⁻⁶ M Inhibition Tauroursodeoxycholic SIGMA- Bile salt 2 × 10⁻⁷ M No Effect acid Aldrich 2 × 10⁻⁶ M No Effect Prostaglandin E2 Biomol Eicosanoid 1 × 10⁻⁷ M Inhibition 1 × 10⁻⁶ M Inhibition Spironolactone SIGMA- 1 × 10⁻⁷ M No Effect Aldrich 1 × 10⁻⁶ M No Effect 1,2-napthoquinone-4- SIGMA- 1 × 10⁻⁶ M No Effect sulfate Aldrich 5 × 10⁻⁶ M No Effect 17β-estradiol SIGMA- Estrogen 1 × 10⁻⁷ M No Effect Aldrich 1 × 10⁻⁶ M No Effect ICI 182,780 TOCRIS Estrogen 1 × 10⁻⁶ M No Effect receptor-α antagonist Lovastatin/Mevinolin SIGMA- Statin, HMG- 1 × 10⁻⁷ M No Effect Aldrich CoA reductase inhibitor PD98059 Calbiochem MEK inhibitor 2 × 10⁻⁶ M No Effect SB203580 Calbiochem P38 inhibitor 2 × 10⁻⁶ M No Effect SB202474 Calbiochem MAPK 2 × 10⁻⁶ M No Effect inhibitor control Parathyroid Hormone Biomol Calciotrophic 1 × 10⁻⁷ M No Effect (1-34) Peptide

FIGS. 7 and 8 illustrate the results obtained for several compounds that blocked BMP-6 mediated induction of SOST expression in hMSC cells. Triamcinolone (Triam), a glucocorticoid analog similar to dexamethasone, blocked the stimulatory effect of BMP-6 on SOST (FIG. 7). Ursodeoxycholic acid (Urso), a bile acid used to treat primary biliary cirrhosis, also blocked the BMP-6 induction of SOST in a dose-dependent manner (FIG. 7). In particular, ursodeoxycholic acid at 3×10⁻⁶ M (Urso-2) completely blocked the induction of SOST by BMP-6 (FIG. 7).

FIG. 8 shows the results of treatment of hMSC cells with fluocinolone acetonide (Fluo) and prostaglandin E2 (PGE2). Both compounds effectively blocked the induction of SOST by BMP-6 whereas other compounds (tauroursodeoxycholic acid, ICI 182,780, estrogen and lovastatin) had minimal effects.

The structures for the five compounds that effectively blocked the induction of SOST expression by BMP-6 are shown in FIG. 9.

These results indicate that 3 different types of glucocorticoid analogs were capable of blocking the induction of SOST expression by BMPs. Other compounds that also blocked SOST expression included bile salts (e.g. ursodeoxycholic acid), and prostaglandins.

Example 4 Exogenously Added Sclerostin Regulates Expression of Osteoblast Function

Individuals with heterozygous or homozygous SOST mutations have a skeletal phenotype characterized by denser and heavier bones (Beighton et al. 1976). In this example: the sclerostin gene product was added to in vitro cultures of osteoblasts. Osteoblastic phenotypic markers were used to monitor the stage of differentiation at which the sclerostin protein affected osteoblastic function.

Determining Effects of Sclerostin Protein on Human Mesenchymal Cells

hMSC cells were plated in 96-well tissue culture dishes at a density of 10,000 cells/cm² in Osteoblast-Inducing medium. Partially purified preparations of baculovirus-expressed sclerostin protein were prepared in sterile PBS using NAP-5 columns prior to use. Human sclerostin protein (0 to 30 μg/ml) or an equal volume of Sf9 conditioned media (Control) was added to cultures of hMSC cells at various times after plating (1 day, 8 days, 15 days, or 21 days). The effects of sclerostin on osteoblastic differentiation were assessed by measuring alkaline phosphatase activity (ALP, determined in cell layers using DEAA buffer (Pierce) containing 0.5% NP-40 and 10 mM p-nitrophenylphosphate), synthesis of collagen type I (Prolagen C ELISA), and calcium deposition for mineralization (colorimetric assay of acid lysates of cell layers, Sigma).

Determining the Effects of Sclerostin Protein on Mouse Mesenchymal C3H10T1/2 Cells

C3H10T1/2 cells (ATCC Deposit No. CCL-226) were plated in 96-well dishes at a density of 25,000 cells per well in complete growth medium (DMEM with high glucose and glutamine supplemented with 10% FCS, 1% penicillin/streptomycin, 0.1 mM non-essential amino acids, 1 mM sodium pyruvate, 55 μM β-mercaptoethanol, and 20 mM HEPES, pH 7.3). C3H10T1/2 cells were used in a short-term (72 hr) assay to determine the effects of human sclerostin protein on BMP-induced ALP activity. Partially purified preparations of bacculovirus-expressed sclerostin protein were prepared in sterile PBS using NAP-5 columns prior to use. Sclerostin protein (0 to 50 μg/ml) or an equal volume of Sf9 conditioned media (control) was pre-incubated with 500 ng/ml BMP-6 for 1 hr prior to addition to cells. For comparison, similar incubations were carried out with anti-BMP-6 antibody and noggin. Cells were harvested 72 hrs later for determination of ALP activity.

To test the specificity of the sclerostin effect, human sclerostin that was synthesized with a FLAG tag, was pre-incubated for 2 hrs at 4° C. with an anti-FLAG antibody coupled to agarose beads. The mixture was then spun down at 10,000×g for 15 minutes at 4° C. and the supernatant treated as “sclerostin protein” in the above assay.

Results

FIG. 10 provides a comparison of the effects of human sclerostin and mouse noggin proteins on alkaline phosphatase (ALP) activity in differentiating hMSC cells. Alkaline phosphatase activity is a phenotypic marker for osteoblast differentiation. After 7 days of treatment, noggin at 1 μg/ml had no effect on alkaline phosphatase activity whereas noggin at 5 μg/ml significantly increased alkaline phosphatase activity (p<0.001 to vehicle-treated cells).

In contrast, under the same conditions, partially purified preparations of human sclerostin consistently decreased alkaline phosphatase activity when administered at either 1 or 5 μg/ml (FIG. 10).

Sclerostin also decreased alkaline phosphatase activity in primary cultures of human osteoblasts (FIG. 11). Osteoblasts that were grown in regular growth media expressed basal levels of alkaline phosphatase (FIG. 11, far right panel); these levels increased significantly when cells were grown in Inducing media (middle panel, darker stain). When a similar group of cells were treated with human sclerostin, there was a marked decrease in the amount of alkaline phosphatase expressed, as evidenced by the reduction in stain (FIG. 11, Sclerostin+Inducing Media).

Sclerostin decreased alkaline phosphatase activity and mineralization in hMSC cells in a dose-dependent manner (FIG. 12). Alkaline phosphatase activity and deposition of mineral (as measured by calcium assay) were significantly decreased in cells treated with increasing concentrations of partially purified preparations of human sclerostin protein but not the control (proteins purified from conditioned Sf9 media) (FIG. 12). Alkaline phosphatase activity and mineral deposition were decreased by about 50% in cells treated with about 10 to 15 μg/ml of the protein (p<0.001 to control).

Synthesis of collagen type I was also decreased in a dose-dependent manner in sclerostin-treated cultures. Partially purified preparations of human sclerostin reduced the synthesis of type I collagen by about 50% in cells treated with 10 μg/mil of the protein (p<0.001 to control, FIG. 13).

To determine the effect of sclerostin protein on the expression of osteoblastic markers in cultures of differentiating hMSC cells, RNA was isolated after a 40-hr treatment and analyzed by RT-PCR (FIG. 14). As can be seen in FIG. 14, RNA levels of markers for adipocytes (PPARγ2) or undifferentiated mesenchymal cells (endoglin) were not affected by treatment with partially purified preparations of human sclerostin protein. On the other hand, RNA levels for osteoblast phenotypic markers such as PTHr, Type I collagen, BMP-2 and BMP-6 were significantly reduced in cells treated with partially purified preparations of human sclerostin protein compared to cells treated with proteins purified from conditioned Sf9 media (control).

BMPs modulate the activity of osteoblasts. Treatment of osteoprogenitor or pre-osteoblasts with BMPs can enhance the activity of markers such as ALP (Gazzero et al., 1998, Nifuji & Noda, 1999). In cultures of hMSC, BMP-6 increased the activity of ALP about 2-fold (FIG. 15). Sclerostin reduced this BMP-induced ALP activity in a dose-dependent manner (ANOVA, p<0.0001). ALP levels In cells treated with BMP-6+30 μg/ml sclerostin were significantly lower than that expressed in BMP-6 treated or vehicle-treated cells (p<0.0001). Indeed, sclerostin also significantly reduced the basal levels of ALP in a dose-dependent manner (ANOVA, p<0.0001).

In FIG. 16, increasing concentrations of BMP-6 partially reversed the inhibitory effect of sclerostin on alkaline phosphatase activity in hMSC cultures.

These findings show that sclerostin interacts with BMPs in regulating osteoblast function.

In mouse mesenchymal C3H10T1/2 cells, ALP activity was increased in a dose-dependent manner by BMP-6 (FIG. 17). The stimulatory effect of BMP-6 on alkaline phosphatase activity in these cells was antagonized by mouse noggin, by partially purified preparations of human sclerostin and by a neutralizing antibody to BMP-6. FIG. 17 shows that mouse noggin decreased BMP-6 stimulated alkaline phosphatase activity with an IC50 of 0.3 μg/ml, data that contrast with the findings of Abe et al (2000). The anti-BMP-6 antibodies decreased BMP-6 stimulated alkaline phosphatase activity by 50% with an IC50 of 0.49 μg/ml. In addition, the partially purified preparation of human sclerostin effectively decreased BMP-6 stimulated alkaline phosphatase activity in a dose-dependent manner, with an IC50 of 10 μg/ml (FIG. 17).

To verify the specificity of the sclerostin response, a human sclerostin fusion protein was prepared that had a FLAG tag fused to the sclerostin coding region. Before addition to mouse mesenchymal C3H10T1 cells, the human sclerostin-FLAG preparation was immuno-depleted with an anti-Flag M2 antibody/agarose complex. As can be seen in FIG. 17, pre-incubation of the sclerostin-FLAG preparation with an anti-Flag antibody/agarose bead complex completely abolished sclerostin antagonism of BMP-6 in the C3H10T1/2 cells. These data indicate that the diminution of BMP-6 induced alkaline phosphatase activity observed upon addition of partially purified sclerostin protein is specifically due to sclerostin, rather than to some unidentified co-purified substance.

Example 5 Sclerostin Causes Apoptosis

Apoptosis is mediated by the activation of a series of cysteine proteases known as caspases (Thornberry & Lazebnik, 1998). Caspases activate proteins such as Bax that promote apoptosis as well as proteins that exhibit protective properties (for example, I-TRAF and Survivin). The initiation of the apoptosis cascade can occur through a number of different mechanisms including the recruitment Of, and the ligand binding to, cell surface Death receptors such as FAS (Vaughan et al. 2002; Budd, 2002). In the present example, the role of sclerostin in the survival of osteoblast Is investigated by incubating hMSC cells with sclerostin and measuring the levels of caspases and other pro-apoptotic factors.

Cell Viability and Apoptosis Assays

Human mesenchymal (hMSC) cells were plated in Osteoblast-inducing media (Biowhittaker's MSCGM medium supplemented with 100 nM dexamethasone, 50 μg/ml ascorbic acid, and 10 mM β-glycerophosphate) at a density of 10,000 cells/cm² in 96-well dishes.

For cell viability assays, cells were treated with a partially purified preparation of bacculovirus-expressed human sclerostin (0 to 20 μg/ml) or an equal volume of a protein preparation purified from Sf9 conditioned media (control) for 1 week. Sclerostin and control were refreshed upon media change. Cells were then lysed and processed using Promega's CellTiterGlo Luminescence Viability Assay.

For apoptosis assays, cells were treated with sclerostin or commercially available preparations of the BMP antagonists noggin, chordin, gremlin or twisted gastrulation (Tsg) for 24 hours prior to assay for caspase activity. In some experiments, cells were treated for various times with a partially purified preparation of baculovirus-expressed human sclerostin (0 to 30 μg/ml) or an equal volume of a protein preparation purified from Sf9 conditioned media (control) in the absence or presence of Calbiochem's caspase inhibitors. Cells were harvested and processed for apoptosis assays using the Homogeneous Caspase ELISA (Roche) or Cell Death (Histone-Associated DNA Fragmentation, Roche).

For apoptosis determination by TUNEL staining, cells were treated for 24 hrs with a partially purified preparation of bacculovirus-expressed human sclerostin (20 μg/ml) or an equal volume of a protein preparation purified from Sf9 conditioned media (control). Cells were fixed with paraformaldehyde and processed using Roche's In Situ Cell Death Detection kit.

In another study, hMSC were treated with vehicle or sclerostin for 6 hrs or 48 hrs. Cells were harvested, RNA prepared and used for the analysis of a commercially available Apoptosis Gene Array (SuperArray, Bethesda, Md.).

Results

FIG. 20 shows the effect of a 7-day treatment of hMSC cells with a partially purified preparation of human sclerostin. Cells were lysed and processed with Promega's CellTiterGlo Viability assay. At this point in time, these cells represent committed osteoprogenitors/pre-osteoblasts. They express high levels of Type I collagen and low levels of alkaline phosphatase. Treatment with increasing concentrations of human sclerostin significantly reduced the number of hMSC cells remaining in the culture compared to cells treated with the control (proteins purified from Sf9 conditioned media).

Treatment of hSMC with sclerostin significantly increased caspase activity (FIG. 21). An inactive preparation of sclerostin (as determined by lack of effects in other biological and biochemical assays) did not significantly affect caspase activity. When commercially available BMP antagonists (noggin, chordin, gremlin, Tsg) were added to hSMC under the same conditions, no increase in caspase activity was observed. These findings show that sclerostin selectively increases the apoptosis of human bone cells.

FIG. 22 illustrates that increasing concentrations of partially purified human sclerostin significantly elevated the activities of caspases as well as the amounts of histone-associated DNA fragments. DNA fragmentation can also be detected by TUNEL staining using commercially available reagents. Increased staining for apoptotic nuclei can be seen in sclerostin-treated as compared to control (proteins purified from Sf9 conditioned media)-treated cells in FIG. 23 (see arrows). Sclerostin decreases the survival of osteoblastic cells by promoting their apoptosis.

Sclerostin treatment of hMSC cells elevated caspase activity for up to 72 hrs (FIG. 24 a). Rat sclerostin) also increased the apoptosis of hMSC cells but to a lesser extent that the human protein (FIG. 24 b).

The induction of caspase activity by sclerostin in hMSC cells could be effectively decreased by commercially available caspase inhibitors (FIG. 25). Caspase-1 inhibitor and Caspase-3 inhibitor effectively blocked the induction of caspase activity by human sclerostin. The combination of the two inhibitors was more potent than either one alone.

To further investigate the effects of sclerostin on the apoptosis of hMSC, RNA was harvested from vehicle and sclerostin-treated cells and used the RNA to probe a cDNA expression array containing apoptosis genes. The results for vehicle and sclerostin-treated samples were compared and data (corrected for background) were expressed as a ratio of sclerostin to vehicle. The data is summarized in the table below.

Incubation Time Gene Function Ratio  6 hrs BAX Proapoptotic 1.53 ± 0.2 Bcl10 Proapoptotic 4.09 ± 2.13 Hrk Proapoptotic 1.59 ± 0.39 Myd88 Proapoptotic  1.4 ± 0.31 Caspase 3 Proapoptotic 2.46 ± 0.69 Caspase 4 Proapoptotic 1.83 ± 1.12 Caspase 7 Proapoptotic 1.76 ± 0.18 XIAP Anti-apoptotic 2.01 ± 0.64 Survivin, IAP2 Anti-apoptotic 1.32 ± 0.48 Bruce Anti-apoptotic 1.45 ± 0.75 48 hrs Bak1 Proapoptotic 2.36 ± 0.74 Blk Proapoptotic 1.83 ± 0.12 Myd88 Proapoptotic 2.64 ± 1.3 Bax Proapoptotic 1.64 ± 0.3 Bcl10 Proapoptotic 1.84 ± 0.76 I-TRAF Anti-apoptotic 2.05 ± 0.54 Casper Anti-apoptotic 2.68 ± 0.28 Mdm2 Anti-apoptotic 1.66 ± 0.34

In hMSC treated for 6 hrs with sclerostin, there was a significant 2 to 4-fold increase in the expression of apoptosis-associated genes such as caspase 3, caspase 4, caspase 7 and the Bcl-2 family members, Bax and Hrk as well as genes involved in cell survival (XIAP, survivin, and Bruce which have been reported to inhibit caspases 3, 7 and 9). By 48 hrs, there was increased expression of proapoptotic members of the Bcl-2 family as well as anti-apoptotic genes (Casper, I-TRAF). Thus treatment of hSMC with sclerostin triggers the induction of proapoptotic as well as anti-apoptotic genes.

In FIG. 25, two commercially available caspase inhibitors (Calbiochem's Caspase-1, Inhibitor VI which blocks caspases 1 and 4, and Caspase-3, Inhibitor I which blocks caspases 3, 6, 7, 8 and 10) blocked sclerostin-induced caspase activities in hMSC cultures. These findings, in addition to those from the apoptosis array, suggest that sclerostin enhances the apoptosis of osteoblastic cells via a FAS-mediated pathway.

Summary

The data shown in these examples demonstrate that sclerostin interacts with BMPs to modulate the activity of osteoblastic cells. This ability of sclerostin to interact with important growth factors is also likely the basis by which it modulates the survival of osteoblasts. By making the growth factors unavailable for cell function, sclerostin may increase the apoptosis of bone cells. Thus agents that block the ability of sclerostin to decrease cell survival and osteoblastic activity offer promise as agents useful in restoring lost bone.

Example 6 Small Interfering RNAs (SiRNAs) to Block Expression of SOST

SiRNAs were designed using the guidelines provided by Ambion (Austin, Tex.). Briefly, the SOST cDNA sequence was scanned for target sequences that had AA dinucleotides. Sense and anti-sense oligonucleotides were generated to these targets (AA+3′ adjacent 19 nucleotides) that contained a G/C content of 35 to 55%. These sequences were then compared to others in the human genome database to minimize homology to other known coding sequences (Blast search).

The target and siRNA sequences designed are provided below.

Target sequence 1: AAGAATGATGCCACGGAAATC (SEQ ID NO:9) Position in gene sequence: 140 GC content: 42.9% Sense strand siRNA: GAAUGAUGCCACGGAAAUCtt (SEQ ID NO:10) Antisense strand siRNA: GAUUUCCGUGGCAUCAUUCtt (SEQ ID NO:11) Target sequence 3: AATGATGCCACGGAAATCATC (SEQ ID NO:12) Position in gene sequence: 143 GC content: 42.9% Sense strand siRNA: UGAUGCCACGGAAAUCAUCtt (SEQ ID NO:13) Antisense strand siRNA: GAUGAUUUCCGUGGCAUCAtt (SEQ ID NO:14) Target sequence 5: AACAACAAGACCATGAACCGG (SEQ ID NO:15) Position in gene sequence: 209 GC content: 47.6% Sense strand siRNA: CAACAAGACCAUGAACCGGtt (SEQ ID NO:16) Antisense strand siRNA: CCGGUUCAUGGUCUUGUUGtt (SEQ ID NO:17) Target sequence 27: AATTGAGAGTCACAGACACTG (SEQ ID NO:18) Position in gene sequence: 950 GC content: 42.9% Sense strand siRNA: UUGAGAGUCACAGACACUGtt (SEQ ID NO:19) Antisense strand siRNA: CAGUGUCUGUGACUCUCAAtt (SEQ ID NO:20) Target sequence 28: AAATGGAAGCATTTTCACCGC (SEQ ID NO:21) Position in gene sequence: 1035 GC content: 42.9% Sense strand siRNA: AUGGAAGCAUUUUCACCGCtt (SEQ ID NO:22) Antisense strand siRNA: GCGGUGAAAAUGCUUCCAUtt (SEQ ID NO:23) Target sequence 30: AAAGTCCAGGGACTGGTTAAG (SEQ ID NO:24) Position in gene sequence: 1093 GC content: 47.6% Sense strand siRNA: AGUCCAGGGACUGGUUAAGtt (SEQ ID NO:25) Antisense strand siRNA: CUUAACCAGUCCCUGGACUtt (SEQ ID NO:26) Target sequence 31: AAGAAAGTTGGATAAGATTCC (SEQ ID NO:27) Position in gene sequence: 1111 GC content: 33.3% Sense strand siRNA: GAAAGUUGGAUAAGAUUCCtt (SEQ ID NO:28) Antisense strand siRNA: GGAAUCUUAUCCAACUUUCtt (SEQ ID NO:29) Target sequence 36: AACTGTAGATGTGGTTTCTAG (SEQ ID NO:30) Position in gene sequence: 1201 GC content: 38.1% Sense strand siRNA: CUGUAGAUGUGGUUUCUAGtt (SEQ ID NO:31) Antisense strand siRNA: CUAGAAACCACAUCUACAGtt (SEQ ID NO:32) Target sequence 40: AATTCTCCTTCGGGACCTCAA (SEQ ID NO:33) Position in gene sequence: 1269 GC content: 47.6% Sense strand siRNA: UUCUCCUUCGGGACCUCAAtt (SEQ ID NO:34) Antisense strand siRNA: UUGAGGUCCCGAAGGAGAAtt (SEQ ID NO:35) Target sequence 47: AAAGAGAGAGAATGAATGCAG (SEQ ID NO:36) Position in gene sequence: 1414 GC content: 38.1% Sense strand siRNA: AGAGAGAGAAUGAAUGCAGtt (SEQ ID NO:37) Antisense stand siRNA: CUGCAUUCAUUCUCUCUCUtt (SEQ ID NO:38) Target sequence 63: AAGAAGCTATGCTGCTTCCCA (SEQ ID NO:39) Position in gene sequence: 1590 GC content: 47.6% Sense strand siRNA: GAAGCUAUGCUGCUUCCCAtt (SEQ ID NO:40) Antisense strand siRNA: UGGGAAGCAGCAUAGCUU (SEQ ID NO:41) Target sequence 70: AAATCACATCCGCCCCAACTT (SEQ ID NO:42) Position in gene sequence: 1726 GC content: 47.6% Sense strand siRNA: AUCACAUCCGCCCCAACUUtt (SEQ ID NO:43) Antisense strand siRNA: AAGUUGGGGCGGAUGUGAUtt (SEQ ID NO:44)

These siRNAs will be tested in vitro and in vivo to ascertain how well they modulate SOST RNA levels.

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All patent and literature references cited in the present specification are hereby incorporated by reference in their entirety. 

1. A method for identifying an antagonist for sclerostin comprising: (a) contacting a cell with sclerostin and a test agent; and (b) detecting whether the test agent prevents sclerostin-induced apoptosis of the cell, wherein a test agent that prevents sclerostin-induced apoptosis of the cell is identified as an antagonist for sclerostin.
 2. The method of claim 1, wherein the test agent is selected from the group consisting of a glucocorticoid or a glucocorticoid analog, an eicosanoid and a bile salt.
 3. The method of claim 2, wherein the glucocorticoid is cortisol.
 4. The method of claim 2, wherein the glucocorticoid analog is selected form the group consisting of dexamethasone, triamcinolone and fluocinolone acetonide.
 5. The method of claim 2, wherein the eicosanoid is prostaglandin E2.
 6. The method of claim 2, wherein the bile salt is selected from the group consisting of ursodeoxycholic acid and tauroursodeoxycholic acid. 